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This  book  is  due  on  the  date  indicated 
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150M/01-92— 941680 


THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

RELATING  TO  SECONDARY  SEXUAL 

CHARACTERS 


By  T.  H.  Morgan 


\ 


Published  by  the  Carnegie  Institution  of  Washington 

Washington,  1919 


CARNEGIE  INSTITUTION  OF  WASHINGTON 

Publication  No.  285 


PRESS   OF   GIBSON   BROTHERS,    INC. 
WASHINGTON,   D.    C. 


CONTENTS. 

Part  I.  page. 

Introduction 5 

Castration  of  Sebrights 6 

A  male  Sebright  that  did  not  become  cock-feathered  after  castration 10 

Transitional  feathers 10 

Castration  of  Fi  hen-feathered  males  from  Sebright  by  game 11 

Castration  of  F2  hen-feathered  males 13 

Hewitt's  Sebright  hen  that  became  cock-feathered  in  old  age 14 

Heredity  of  hen-feathering 14 

Heredity  of  color  in  the  cross  between  Sebright  and  Black-Breasted  Game  bantam.  17 

A.  The  Fi  birds 18 

B.  Description  of  F2  birds 19 

C.  Back-cross  of  Fi  to  game 21 

D.  The  number  of  color  factors  involved 22 

E.  Back-cross  of  Fi  9  to  Sebright  c? 23 

F.  Review  of  the  heredity  of  the  color  of  the  plumage  in  poultry 23 

Endocrine  cells  in  ovary  and  testes  of  birds 32 

Luteal-cells  in  the  testes  of  the  male  Sebright 34 

Endocrine  cells  in  the  testes  of  mammals 35 

Cyclical  changes  in  the  interstitial  cells  in  hibernating  mammals 36 

Hermaphroditism  in  poultry  and  the  secondary  sexual  characters 37 

Part  II. 

Darwin's  theory  of  sexual  selection 43 

Other  theories  to  account  for  secondary  sexual  characters 45 

Display  of  the  male 50 

Part  III. 

The  genetic  and  the  operative  evidence 62 

A.  Evidence  from  mammals 

B.  Evidence  from  birds 

C.  Evidence  from  amphibia sr> 

D.  Evidence  from  crustaceans 

E.  Evidence  from  insects 92 

Part  IV. 

Summary  and  conclusions 

Bibliography 

Description  of  plates 106 

3 


{  in 


THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE  RELATING 
TO  SECONDARY  SEXUAL  CHARACTERS. 


By  T.  H.  Morgan. 


PART  I. 


There  are  a  few  races  of  poultry  that  have  two  kinds  of  males,  one 
with  the  feathering  of  the  ordinary  cock,  the  other  with  the  feathering 
of  the  hen.  The  Hamburgs  and  the  Campines  are  perhaps  the  best 
known  races  of  this  sort.  Convention  amongst  breeders,  in  certain 
countries,  has  determined  that  the  cock-feathered  bird  shall  be  the 
standard,  and  at  other  times  and  places  that  the  hen-feathered  males 
shall  be  the  show  birds.  In  one  breed,  at  least,  viz,  the  Sebright 
bantams,  the  hen-feathered  cock  is  the  only  known  type.  Cock- 
feathered  Sebrights  have  never  been  seen,  so  far  as  I  know.  This 
breed  is  pure  for  hen-feathering.  As  shown  in  plate  1,  figure  3,  the 
male  Sebright  lacks  the  long,  pointed  saddle  feathers  at  the  base  of 
the  tail  of  the  common  cock,  also  the  peculiar  back  and  neck  feathers 
(hackles)  of  the  cock  bird,  as  well  as  the  male  feathering  on  the  bow 
of  the  wing.  His  feathers  in  these  parts  are  almost  exactly  like  those 
of  the  hen  (plate  4,  fig.  4).  The  long  sickle  feathers  covering  the  true 
tail  are  also  absent,  although  the  two  median  ones  sometimes  occur 
in  males  of  this  race. 

The  Sebrights  seemed  excellent  material  for  studying  the  heredity 
of  this  type  of  plumage  in  the  male.  In  1911  I  began  to  study  this 
problem,  and  crossed  Sebrights  to  Black-Breasted  Game  bantams. 
The  latter  race  was  chosen  not  only  because  the  males  have  the  typical 
cock-feathering,  but  also  because  the  coloration  of  these  birds  resembles 
very  closely  that  of  the  jungle-fowl,  from  which  many,  perhaps  all,  of 
our  domesticated  races  have  sprung. 

In  dissecting  some  of  the  F2  birds  from  this  cross  I  noticed  that  the 
testis  of  the  male  was  often  more  flattened  than  is  the  testis  of  the 
typical  male  bird,  that  it  was  often  somewhat  pear-shaped,  and  that 
frequently  it  was  in  part  or  entirely  black.  Recalling  that  male 
Sebrights  are  said  to  be  often  partially  sterile,  the  idea  naturally 
suggested  itself  that  these  birds  are  hen-feathered  because  the  testes 
have  assumed  some  of  the  characteristics  of  the  ovary.  It  had  long 
been  supposed,  and  had  been  finally  established  by  Goodale,  that  the 
presence  of  the  ovary  in  the  female  suppresses  her  potential  develop- 
ment of  plumage,  for  when  the  ovaries  of  the  hen  are  diseased  or 
removed  she  develops  the  plumage  of  the  male.  This  reasoning  led 
me  to  try  the  experiment  of  castrating  the  hen-feathered  males  in 

5 

D.  H.  HILL  LIBRARY 
Ncrih  Carolina  State  College 


6  THE    GENETIC    AND    THE    OPERATIVE    EVIDENCE 

order  to  see  if  they  would  become  cock-feathered.  The  outcome  was 
immediately  apparent;  the  new  feathers  were  those  of  the  cock  bird. 
While  the  " reasoning"  that  led  to  the  experiment  is  open  to  serious 
question,  nevertheless  the  "hint"  furnished  by  the  unusual  condition 
of  the  testis  led  finally  to  the  discovery  that  luteal  cells  were  present 
in  abundance  in  the  testes  of  the  male  Sebright  like  those  present  only 
in  the  females  of  other  breeds.  Whether  or  not  the  shape  of  the  testis 
of  the  Sebright,  that  is  sometimes  like  that  of  the  ovary,  is  connected 
with  the  unusual  abundance  of  luteal  cells  in  the  testis  I  do  not  know. 
If  so,  then  the  hint  that  came  from  their  shape  was  not  so  unreasonable 
as  appears  at  first  sight. 

The  birds  first  operated  upon  were  adult  Fi  and  F2  hen-feathered 
birds.  The  first  one  done  by  myself  died,  but  a  few,  whose  testes  were 
removed  by  Dr.  H.  D.  Goodale  at  my  request,  lived  and  changed  to 
cock-feathered  birds.  Since  then  I  have  operated  successfully  on  a 
number  of  Fx  and  F2  birds,  as  well  as  Sebright  males.  In  these  opera- 
tions I  have  had  throughout  the  assistance  of  Dr.  A.  H.  Sturtevant 
and  for  two  years  the  assistance  of  Dr.  J.  W.  Gowen  also.  I  wish  to 
express  my  appreciation  of  their  help  and  advice,  for  without  it  I 
doubt  whether  I  could  have  carried  out  the  work  successfully.  Since 
the  main  interest  attaches  to  the  Sebright  experiments,  they  will  be 
described  first,  although  they  were  the  last  to  be  performed. 

CASTRATION  OF  SEBRIGHTS. 

Except  for  the  similarities  of  the  plumage,  the  male  Sebright  differs 
as  much  from  the  female  as  do  cocks  of  other  races.  The  rose  comb 
is  very  large  in  the  male,  small  in  the  female  (plate  4,  figs.  3,  4).  The 
wattles  also  are  longer  in  the  male.  The  cock  carries  himself  erect, 
as  do  the  males  of  other  breeds.  His  spurs  are  well  developed  and 
he  shows  the  aggressive  behavior  of  his  sex.  On  the  other  hand,  the 
shortness  of  the  feathers  on  the  back  of  the  neck  (the  hackles),  the 
absence  of  the  pointed  feathers  on  the  back  and  rump,  and  the  usual 
absence  of  long  sickles  and  other  tail-covert  feathers  make  him 
hen-like.  The  detailed  account  of  the  feathers  in  these  critical  regions 
will  be  given  when  comparisons  are  made  with  the  feathers  of  the 
castrated  birds  (plates  6  and  8). 

Six  males  have  been  successfully  operated  upon  and  with  one 
apparent  exception  have  all  given  the  same  results.  The  birds  were  of 
somewhat  different  ages ;  they  had  been  hatched  about  July,  and  were 
operated  upon  about  November  of  the  same  year,  when  they  were 
either  half  grown  or  had  nearly  reached  maturity.  At  the  time  of  the 
operation  a  few  feathers  were  removed  from  different  regions  of  the 
body,  and  the  new  feathers  that  regenerated  in  the  course  of  3  or  4 
weeks  showed  all  the  characteristics  of  those  that  came  in  later  to 
replace  the  juvenile  or  first  adult  coat.    These  regenerated  feathers  do 


RELATING   TO    SECONDARY    SEXUAL    CHARACTERS.  7 

not,  therefore,  call  for  special  notice.  All  of  the  new  feathers  were  in 
shape,  pattern,  and  general  coloration  strikingly  different  from  the 
original  feathers,  some  of  which  were  at  first  still  present,  the  old 
feathers  of  course  showing  no  change. 

After  completely  molting,  the  appearance  of  the  birds  may  be 
gathered  from  the  photographs  (plate  5)  and  from  the  colored  drawings 
(plates  1  and  3).  The  male  now  has  in  all  points  the  plumage  of  a 
typical  cock-feathered  male  bird  of  other  breeds.  This  is  startlingly 
apparent  in  the  hackle,  back,  rump,  sickle,  and  tail-covert  feathers. 
Instead  of  the  laced  feathers  that  are  characteristic  of  both  male  and 
female,  the  whole  upper  surface  of  the  bird  appears  reddish  or  yellowish, 
the  black  marginal  edging  of  the  feathers  having  disappeared.  A 
detailed  comparison  of  the  feathers  of  the  different  regions  will  show 
how  great  a  change  has  taken  place.     (See  page  8.) 

In  plates  6  and  8  the  feathers  from  characteristic  regions  of  the 
normal  Sebright  and  of  the  castrated  Sebright  are  shown  in  pairs. 

One  of  the  first  Sebrights  that  was  castrated  was  a  lighter  bird  than 
the  others.  Its  lighter  color  was  partly  due  to  the  narrower  outer 
band  of  the  laced  feathers,  (plate  6,  figure  1,)  and  partly  to  the 
lighter  color  of  the  yellow-brown  center  of  the  feathers.  The  bird  had 
a  single  comb,  but  as  this  crops  up  occasionally  in  some  stocks  of 
Sebrights,  it  need  not  be  interpreted  to  mean  that  the  bird  was  impure 
for  color  factors.  After  being  castrated  the  bird  changed  over  com- 
pletely to  cock-feathering  and  has  remained  in  that  condition  for  two 
or  more  years.  As  shown  in  plate  5,  figure  2,  the  plumage  is 
even  more  fully  developed  than  in  cock  birds  of  some  other  breeds. 
The  comb  and  wattles  are,  however,  shrunken  and  pale,  as  in  a  capon. 
The  bird  is  timid  and  scarcely  or  never  crows.  When  killed  (May 
1919)  no  pieces  of  testes  and  no  trace  of  testicular  tissue  at  the  old 
situs  were  found. 

The  details  of  the  feathers  are  shown  in  plate  6,  figures  1  and  la, 
where,  in  each  instance,  one  of  the  old  and  one  of  the  new  feathers 
from  the  same  region  are  placed  side  by  side.  The  feathers  on  the 
head  and  hackle  are  yellow,  even  to  the  base.  At  the  base  of  the 
hackle — the  so-called  cape — a  few  feathers  have  a  small  black  tip. 
The  feathers  of  the  back  are  entirely  yellow,  except  that  where  the 
fluff  begins  there  is  some  dark  pigment.  The  saddle  feathers  are  for 
the  most  part  all  yellow,  but  a  few  have  at  the  base,  near  the  fluff, 
black  on  each  side.  The  tail  coverts  are  long,  with  a  black  margin  at 
their  tip.  The  tail  feathers  are  long,  mossy,  and  have  a  black  tip. 
The  wing-bow  feathers  are  all  yellow,  except  the  black  fluff  at  the  base. 
The  feathers  on  the  crop  are  mostly  yellow  with  black  margin  around 
the  end.  Those  on  the  breast  lower  down  are  yellow  with  black  tip 
and  black  fluff. 

There  was  another  Sebright  operated  upon  at  the  same  time  that  was 
a  darker  bird  (as  the  original  feathers  show,  plate  8,  figs.  1  to  4).    It  had 


8 


THE    GENETIC   AND   THE    OPERATIVE   EVIDENCE 


a  rose  comb.  The  feathers  that  were  plucked  at  the  time  of  operation 
were  replaced  at  once  by  new  feathers  of  the  cock-feathered  type.  The 
new  feathers  that  came  in  as  the  old  ones  were  molted  were  also  cock- 
type,  and  the  bird  soon  assumed  the  complete  characteristic  cock- 
feathering.    The  comb  was  shrunken  as  in  castrated  birds  (plate  5, 


SEBRIGHT. 
Plates  6  and  8. 

1.  On  the  head  (a)  the  feathers  are  small, 

dull  black  with  lighter  margin  and 
reddish  quill. 

2.  On  the  hackle  (b)  the  feathers  are  yellow 

bordered  with  black,  expecially  at 
the  base,  and  at  the  tip  outside  of 
this  border  there  is  a  narrow  yellow 
border  (broader  at  base).  The 
border  is  absent  at  tip. 

3.  In  the  middle  of  the  back  (between  the 

wings)  the  feathers  are  yellow  with 
black  margin  at  the  tip.  At  the 
base  there  is  some  dark  color. 


4.  The  saddle  is  made  up  of  typical  laced 

feathers  with  black  where  the 
fluff  begins. 

5.  The  tail  coverts  are  short;  the  upper 

ones,  especially  the  short  sickles, 
are  slightly  curved.  The  sickle 
feathers  extend  up  only  about  half 
the  length  of  the  tail.  They  are 
yellow,  laced,  and  have  a  black 
margin,  tending  to  be  lost  at  tip. 


6.  The  yellow  tail  is  short  and  erect. 


7.  The  feathers  on  the  wing  bow  are  prac- 

tically like  those  on  the  back,  but 
shorter. 

8.  Over  the   crop    and    lower   breast   the 

feathers  are  laced. 


CASTRATE. 
Plates  6  and  8. 

1 .  Feathers  entirely  yellow  and  more  slender. 

Those  on  each  side  of  the  shrunken 
comb  stand  up  from  the  head. 

2.  Hackles  on  upper  part  of  neck  have  a 

black  base  with  red  tip.  The 
outer  edge,  without  barbules,  is 
narrow,  then  broader  than  at  tip. 
Farther  down  the  neck  the  edge 
with  barbules  is  yellow  with  a 
narrow  black  margin. 

3.  In  the  part  of  the  feather  with  barbules 

there  is  a  yellow  center  bordered 
by  a  broad  black  band,  especially 
at  base.  In  the  part  without  bar- 
bules the  feathers  are  yellow  and 
more  pointed.  This  region  espe- 
cially is  deeper  yellow  than  in  the 
original  Sebright. 

4.  Saddle   consists  of  long,   slender  laced 

feathers,  except  at  tip,  which  is  red. 
Barbules  are  absent  along  edge  of 
outer  third  of  feather. 

5.  Tail  coverts  long,  covering  the  tail  as  in 

cock  birds  of  other  breeds.  The 
sickle  feathers,  especially  the  upper 
ones,  are  much  curved,  with  black 
tips;  the  black  margin  is  largely 
gone.  The  feathers  are  mossy, 
sometimes  splotched  (this  is  also 
sometimes  noticeable  in  normal 
birds) . 

6.  The  tail  feathers  themselves  are  almost 

twice  as  long  as  in  normal  bird;  the 
upper  feathers  are  more  curved. 

7.  The  feathers  of  wing  bow  are  like  those  of 

the  back  of  the  same  bird,  but 
shorter. 

8.  The  crop  feathers  are  narrower,  with  a 

wider  black  margin,  and  a  few  may 
be  also  entirely  black.  Feathers 
on  lower  breast  much  like  those  in 
normal,  but  a  little  more  pointed. 


figure  5).  During  the  spring  of  1917  it  was  noticed  that  the  bird  was 
going  back  towards  the  hen-feathered  type,  and  by  the  end  of  the  summer 
he  was  in  the  intermediate  condition,  as  shown  by  the  photograph  and 
by  the  individual  feathers  (plate  8,  lb,  2b,  3b,  46) .  The  comb  had  begun 
to  enlarge  also.  The  bird  was  opened  again  (1918)  and  pieces  of  testis 
about  as  big  as  peas  were  found  on  one  side.    Evidently  a  piece  of  the  old 


RELATING   TO   SECONDARY   SEXUAL   CHARACTERS.  9 

testis  had  been  left  behind  and  had  regenerated.  As  it  enlarged  the  new 
feathers  were  affected  so  that  the  plumage  returned  towards  the  normal 
type.  The  pieces  of  testis  were  removed  and  a  few  feathers  plucked 
out.  The  new  feathers  that  came  in  were  typically  cock-feathered, 
and,  as  the  molting  proceeded  during  the  winter  and  spring,  the  bird 
became  cock-feathered  for  a  second  time  as  shown  in  photograph 
(plate  5,  figure  6)  and  by  the  feathers  in  plate  8,  lc,  2c,  3c,  4c.  Here, 
then,  is  an  excellent  example  of  the  connection  between  the  gonad  and 
the  condition  of  the  plumage.  On  opening  this  bird  (May  1919)  no 
pieces  of  testes  were  found.  There  was  a  very  small  whitish  lump  at 
the  situs  of  the  old  testes,  which,  when  sectioned,  showed  some  gland- 
ular-like tissue,  not  in  tubules,  and  no  evidence  of  testicular  tissue. 

Three  other  younger  Sebrights  of  the  same  stock  were  successfully 
castrated.  They  were  hatched  in  June  or  July  and  castrated  in 
November  of  the  same  year.  They  remained  quite  small  birds,  despite 
their  elongation  due  to  the  long  tail  and  tail  coverts  that  they  devel- 
oped. One  of  these  birds  in  his  cock-feathered  plumage  is  shown  in 
plate  3,  figure  1."  One  has  died,  the  other  two  are  alive  and  markedly 
cock-feathered,  as  shown  in  plate  6,  figure  2a.  All  three  birds  were 
dark  red-brown,  much  more  so  than  the  two  preceding  cases,  especially 
the  first  case.  This  color  difference  might  be  attributed  to  the  earlier 
age  of  the  three  birds  when  operated  upon,  or  to  a  more  complete 
(or  less  complete)  operation  involving  perhaps  neighboring  parts,  or 
to  the  birds  having  a  somewhat  different  genetic  composition  (t.  e., 
modifying  factors).  -  There  is  no  special  reason  why  the  operation  if 
performed  early  should  have  a  different  result  on  feathers  that  develop 
after  the  bird  is  of  adult  age.  Goodale  has  suggested  that  there  may 
be  organs  in  the  vicinity  of  the  testis  that  have  some  influence  on  the 
kind  of  plumage  produced,  and  if  there  are  such  organs  they  might  be 
removed  in  one  bird  and  accidentally  left  in  another.  It  would  not, 
however,  be  probable  that  the  bird  operated  on  at  first  had  received 
one"  treatment  and  the  later  ones  the  other  treatment.  It  seems  to  me 
more  probable  that  the  birds  have  come  from  different  genetic  strains, 
and  that  this  genetic  difference  gives  a  more  plausible  explanation 
of  the  darker  cock-feathered  plumage.  Goodale  observed,  for  the  first 
time  I  think,  that  the  largest  wing  coverts  of  the  castrated  cock  be- 
come longer.  I  looked,  therefore,  with  some  interest  at  the  condition 
of  these  same  feathers  in  the  castrated  Sebrights.  As  shown  in  plate 
10,  figures  1,  la,  these  feathers  are  also  longer  and  narrower  in  the  cas- 
trated Sebright  than  in  the  normal  bird. 

The  true  tail  feathers  of  the  capon  are  said  to  be  longer  than  those  of 
the  cock.  This  holds  also  for  the  tail  feathers  of  all  of  my  castrated 
Sebrights.  Their  true  tail  feathers  are  considerably  longer  than  those 
of  the  normal  male,  as  seen  by  pulling  them  out  and  comparing  the 
two.  Their  length  is  concealed  while  on  the  bird  by  the  excessively 
long  coverts  that  appear  after  castration. 


10  THE    GENETIC    AND    THE    OPERATIVE    EVIDENCE 

In  1916  I  operated  on  a  Sebright  male  that  lived  for  some  months, 
but  died  in  the  summer  of  1917.  At  the  time  of  his  death  he  had 
assumed  a  partial  cock-feathering,  as  shown  by  the  feathers  in  plate  9, 
figure  3,  3a.  Dissection  showed  that  some  of  the  testes  had  been  left, 
and  as  is  then  to  be  expected,  the  change  was  incomplete. 

A  MALE  SEBRIGHT  THAT  DID  NOT  BECOME  COCK-FEATHERED 

AFTER  CASTRATION. 

One  of  the  males  that  had  been  castrated  with  the  others  did  not 
become  cock-feathered  even  after  a  year.  Taking  for  granted  that 
the  castration  had  been  incomplete,  the  bird  was  opened,  but  as  no 
pieces  of  the  testes  were  to  be  found  in  the  normal  position  he  was 
killed  and  carefully  dissected.  There  were  no  pieces  of  testes  found 
in  the  normal  situs.  A  small  whitish  patch  of  material  from  this  region 
was  cut  into  sections,  but  no  testicular  material  was  found  in  it.  Then 
a  large  piece  of  the  back  from  the  region  of  the  attachment  of  the 
testes  was  prepared,  but  as  yet  this  piece  has  not  been  sectioned.  Even 
were  a  small  piece  of  tissue  to  be  found,  it  would  seem  unlikely  that  it 
would  suffice  to  hold  back  all  indications  of  the  cock-feathering,  for 
after  incomplete  removal  of  the  testis  there  are  nearly  always  at  first 
some  indications  of  the  lack  of  material.  The  most  plausible  view  here 
is  either  that  some  other  gland  may  have  assumed,  provisionally,  the 
function  of  the  missing  testes,  or  else  a  detached  piece  has  not  yet 
been  found.  Glandular  cells  like  the  luteal  cells  of  the  ovary  have 
in  fact  been  described  by  some  observers  in  other  organs. of  the  body. 
As  yet  I  have  not  found  time  to  make  a  thorough  histological  study 
of  the  tissues  of  this  bird. 

TRANSITIONAL  FEATHERS. 

In  several  birds  new  feathers  had  begun  to  develop  at  the  time  of 
the  operation  under  the  influence  of  the  testicular  secretion.  After 
the  removal  of  the  testes,  these  feathers  continued  to  grow  and  in  the 
absence  of  the  original  conditions  changed  over  to  the  other  type. 
The  outer  end  of  these  feathers  shows  the  original  or  normal  shape  and 
color,  while  the  inner  end  shows  the  new  characteristics.  Such  feathers 
have  been  seen  in  nearly  all  of  my  castrated  birds;  a  few  from  the 
Sebright  will  suffice  by  way  of  illustration.  In  plate  10,  figure  2a, 
four  such  transitional  feathers  are  shown.  In  a  and  b  two  feathers 
from  the  hackle  are  photographed.  The  first  (a)  had  begun  as  a  normal 
Sebright  hackle  feather,  as  seen  in  the  condition  of  its  tip;  the  rest  of 
the  feather  is  the  same  as  the  feather  of  the  castrated  bird.  For  com- 
parison with  this  feather,  two  (2b)  from  the  same  bird  are  shown  that 
began  to  develop  after  the  testes  were  removed,  i.  e.,  at  the  same  time 
as  the  change  occurred  in  the  former  feather.    At  the  time  the  latter 


RELATING   TO    SECONDARY    SEXUAL    CHARACTERS.  11 

feather  (b)  had  not  yet  completed  its  full  growth.  On  the  bow  of  the 
wing  a  few  intermediate  feathers,  like  the  one  shown  in  2a,  were 
present.  (For  comparison  with  normal  and  castrated  feathers  see 
those  on  plates  6  and  8.) 

An  intermediate  feather  from  the  back  is  shown  in  2a.  For  com- 
parison with  the  old  feathers  from  the  same  region  see  plate  6,  fig.  2. 
An  intermediate  saddle  feather  is  shown  in  2a.  For  comparison  with 
normal  feathers  from  the  same  region  see  figure  2.  A  still  later  feather 
from  the  castrated  bird  is  shown  in  2b.  The  last  was  not  yet  com- 
plete when  removed  from  the  bird. 

It  will  be  noticed  that  the  change  after  castration  involves  the  color, 
the  shape,  and  the  presence  and  absence  of  barbules  in  those  parts  of 
the  bird  that  are  peculiar  in  the  last  respect.  The  transition  in  these 
characters  is  quite  sharp — as  sharp  in  'fact  as  is  compatible  with  the 
passage  from  one  structure  to  that  of  an  entirely  different  kind  without 
any  discontinuity  of  growth.  Owing  to  the  quickness  of  the  response 
shown  by  the  feather,  it  will  be  possible  to  study  more  in  detail  the 
length  of  time  the  secretion  remains  in  the  body  of  the  bird  after  the 
testes  have  been  removed. 

CASTRATION  OF  F,  HEN-FEATHERED  MALES  FROM  SEBRIGHT 

BY  GAME. 

Hen-feathering  is  dominant  to  cock-feathering.  As  shown  in  plate 
2,  the  Fx  male  is  almost  as  completely  hen-feathered  as  is  the  male 
Sebright.  There  is  a  somewhat  greater  color  difference  between  the 
Fi  male  and  Fi  female  than  between  the  Sebright  male  and  female. 
Two  Fi  birds  were  castrated  for  me  by  Goodale.  At  the  time  of 
operation,  in  the  autumn  of  1916,  both  birds  were  full  grown,  (plate 
2,  figure  1).  After  molting  the  old  feathers,  both  birds  appeared  as 
shown  in  plate  2,  figure  4.  Each  is  completely  cock-feathered.  The 
plumage  has  also  undergone  a  remarkable  change  in  color.  In  general, 
the  color  change  is  from  yellow  and  black  to  reddish  yellow.  The 
greatest  change  is  over  the  upper  surface.  The  sickle,  covert,  and  tail 
feathers  are  well  formed  and  have  now  become  iridescent  black.  The 
breast  has  changed  least  of  all.  One  bird  died  February  12,  1919. 
When  opened  there  was  found  on  the  left  side  a  small  white  lump ; 
on  the  other  side  almost  nothing.  The  lump  was  found  to  consist  of 
testicular  tubules  with  loose  glandular  cells  on  its  walls. 

The  extent  to  which  the  change  has  taken  place  is  best  shown  by 
comparison  of  individual  feathers  from  identical  regions — one  before 
and  one  after  the  new  feathers  (taken  out  two  years  later)  have  conic 
in  (plate  7).  The  contrast  between  the  old  and  new  feathers  of  the 
hackle,  saddle,  back,  and  wing-bow  are  the  most  striking.  In  all  of 
these  the  new  feathers  have  become  red  on  the  exposed  portion  and  the 
margin  is  free  from  barbules,  as  in  the  cock  bird.    The  increase  in  size 


12 


THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 


and  change  in  shape  of  these  feathers  is  remarkable.  Equally  great 
is  the  change  in  the  tail-coverts  that  grade  into  those  of  the  saddle 
at  the  base.  The  two  median  coverts  or  sickle  feathers  are  longer  than 
the  tail  and  much  arched.  They  are  jet  black  with  a  purplish  irides- 
cence and  with  a  yellow-red  shaft.  The  tail  itself  has  also  changed; 
it  has  lost  its  stippling,  and  has  become  black  like  the  coverts.  The 
increase  in  length  of  the  tail  feathers  is  as  remarkable  as  the  increase 
in  length  of  the  coverts.     A  detailed  account  of  these  changes  follows : 


1.  The  head  feathers  are  yellow  with  black 

base  that  shows  through  on  the 
head. 

2.  The  hackle  feathers  are  yellow  with  black 

base  (showing  through  on  neck). 

3.  The  red  feathers  of  the  back  are  penciled. 

There  is  a  black  band,  especially 
around  tip  just  inside  of  the 
margin. 

4.  The  saddle  feathers  are  much  like  those 

of  the  back,  much  stippled  in  cen- 
ter.    The  border  is  more  distinct. 

5.  The  tail  coverts  are  similar  to  those  of 

the  hen. 

6.  The  tail  feathers  are  black,  and  with 

exception  of  the  lower  feathers  they 
are  partly  stippled. 

7.  The  wing-bow  feathers  are  penciled  like 

those  of  the  back. 

8.  Feathers  on  crop  yellow  with  black  spot 

at  tip;  those  lower  down  on  breast 
have  a  bigger  spot. 


CASTRATE. 
1.  The  feathers  are  entirely  red. 


2.  The  hackle  feathers  are  entirely  red. 

3.  Feathers  of  back  are  red  except  for  black 

at  base.     Barbules  absent  at  end 
and  side.     Tip  pointed. 

4.  The  saddle  feathers  are  red  with  black 

base.     They  are  long  and  pointed. 

5.  The  coverts  are  blue-black,  with  brown 

shaft.     They    are    long,    pointed, 
and  curved. 

6.  The  tail  feathers  are  black,  not  stippled, 

and  have  a  black  shaft. 

7.  The   wing-bow   feathers   are   red   with 

black  base. 

8.  Over  the  crop  the  feathers  are  orange- 

brown;  on  the  breast  they  have  the 
same  color  and  a  small  black  tip. 


The  Fi  bird  from  which  the  colored  drawing  (plate  2)  was  made 
and  from  which  the  normal  Fi  feathers  were  pulled  was  lent  to  Dr. 
Goodale  in  the  summer  of  1917.  The  bird  died  in  April  1918,  and  his 
skin  was  sent  to  me.  He  also  had  begun  to  change  over  to  cock- 
feathering  (plate  9,  figures  2,  2a).  Goodale  recorded  that  the 
testis  had  dwindled  to  small  bodies  only  about  10  by  5  mm.  This 
accounts  for  the  change  to  cock-feathering.  For  comparison  I  have 
added  a  third  set  of  feathers  to  the  two  former  sets,  showing  the  new 
hackle,  back,  saddle,  wing,  and  bow  feathers  of  this  bird.  The  feathers 
show  that  the  change  is  in  the  same  direction  as  that  shown  by  the 
castrated  cock,  but  it  has  not  gone  so  far  in  the  direction  of  cock- 
feathering.  The  tail  is  still  short  and  the  feathers  are  black.  The 
sickle  feathers  are  not  longer  than  the  tail  and  are  stippled.  It  is 
probable  that  this  is  the  old  tail  whose  feathers  have  not  been  molted 
since  the  testis  dwindled.  In  fact,  elsewhere  the  old  and  the  new 
feathers  are  both  present,  showing  that  a  complete  molt  had  not  taken 
place.  The  old  feathers  still  present  are  practically  like  those  of  the 
original  Fx  bird,  showing  that  the  change  was  of  recent  date,  and  due 
to  the  decrease  in  the  testis  which  was  probably  caused  by  disease. 


RELATING    TO    SECONDARY    SEXUAL    CHARACTERS.  13 

CASTRATION  OF  F2  HEN-FEATHERED  MALES. 

The  F2  hen-feathered  males  from  this  cross  could  not  be  utilized  until 
they  had  begun  to  assume  the  adult  plumage,  since  before  that  time 
they  were  like  the  cock-feathered  F2  males.  Consequently,  the  opera- 
tion is  more  difficult  and  more  dangerous  to  the  bird.  A  good  many 
birds  have  died  in  consequence  of  the  operation,  but  enough  successful 
operations  (five)  were  made  to  show  what  the  color  of  certain  types  of 
hen-feathered  bird  would  be  when  changed  to  cock-feathering. 

A  hen-feathered  male  (No.  292)  that  was  darker  than  the  F!  male — 
in  fact,  almost  black,  except  for  a  yellow  center  in  some  of  the  dorsal 
feathers  that  were  mossy  or  penciled —  was  castrated.  The  details 
of  characteristic  feathers  may  be  gathered  from  the  feathers  in  plate  7, 
figure  2.  A  corresponding  set  of  the  new  feathers  after  castration,  2a, 
are  paired  with  the  former.  The  castrated  male  in  his  new  plumage 
is  shown  in  plate  2,  figure  3.  His  dorsal  surface  is  colored  very  much 
as  is  the  same  region  in  the  Fx  bird,  but  the  breast  is  very  much 
darker,  so  that  the  bird  as  a  whole  presents  a  very  different  appearance 
from  the  FL  castrated  male.  A  very  small  white  mass  was  found 
when  the  bird  was  killed  in  place  of  the  old  testis,  composed,  in  sec- 
tions, of  a  reticulated  mass  of  cells  that  look  like  old  broken-down 
follicles  of  testicular  tubules  with  a  few  cell-layers  lining  the  tubules. 

An  F2  male  (68)  also  had  dark  feathers  (plate  3,  figure  2,  and  plate 
9,  figure  1) .  The  castrated  male  in  his  new  plumage  is  represented  in 
plate  3,  figure  3.  Here  again  the  upper  surface  is  much  like  that  of  the 
last  castrate,  and  also  like  that  of  the  Fi  castrate.  The  breast  has 
changed  much  less  than  the  back ;  the  centers  of  the  feather  are  brown 
with  a  black  margin  and  a  black  band  at  the  tip.  The  exposed 
portion  of  the  secondaries  and  the  coverts  are  not  so  brown  as  in  the 
last  bird.  The  spurs  of  this  bird  were  bent  back,  looking  like  the 
horns  of  a  ram.  When  killed  and  examined,  several  small  white  pieces, 
that  looked  like  pieces  of  testes,  were  found  in  the  abdominal  cavity 
near  the  old  attachment  of  the  testis.  A  histological  study  showed  that 
these  pieces  contained  tubular  tissue  apparently  testicular,  but  with- 
out germ-cells. 

Another  F2  male  (Band  No.  221)  was  yellow  in  general  color,  the 
feathers  being  irregularly  penciled.  After  castration  (plate  3,  figure  4) 
the  bird  became  red  above  and  deep  brown  below;  the  tail  and 
coverts  were  black. 

A  pale-yellow  hen-feathered  bird  (No.  218)  was  also  castrated. 
Here  also  the  change  was  most  conspicuous  over  the  upper  surface, 
not  only  in  a  greater  depth  of  color  than  elsewhere,  but  in  the  shape, 
etc.,  of  the  feathers.  On  the  breast  the  original  yellow  color  remains, 
but  is  slightly  deepened.  When  killed  and  opened  (May  14,  1919), 
a  few  small,  whitish  pieces  were  found.  When  these  were  sectioned  it 
was  seen  that  they  were  made  up,  for  the  most  part,  of  tubules  look- 


14  THE    GENETIC    AND    THE    OPERATIVE    EVIDENCE 

ing  like  those  of  the  epididymis  and  also  a  few  testicular  tubules. 
At  the  old  situs  there  were  some  regenerated  lumps,  which  in  sections 
appeared  to  be  loose  glandular  tissue.  No  germ-cells  were  present  and 
the  tissue  just  referred  to  may  be  old  testicular  tubules. 

HEWITT'S  SEBRIGHT  HEN  THAT  BECAME  COCK-FEATHERED 

IN  OLD  AGE. 

Darwin  records  in  Chapter  XIII  of  Animals  and  Plants  under 
Domestication  a  change  that  took  place  in  an  old  female  Sebright : 

"Mr.  Hewitt  possessed  an  excellent  Sebright  gold-lace  bantam  hen,  which, 
as  she  became  old,  grew  diseased  in  her  ovaria  and  assumed  male  characters. 
In  this  breed  the  males  resemble  the  females  in  all  respects  except  in  their 
combs,  wattles,  spurs,  and  instincts;  hence  it  might  have  been  expected  that 
the  diseased  hen  would  have  assumed  only  those  masculine  characters  which 
are  proper  to  the  breed,  but  she  acquired,  in  addition,  well-arched  tail  sickle- 
feathers  quite  a  foot  in  length,  saddle-feathers  on  the  loins,  and  hackles  on  the 
neck — ornaments  which,  as  Mr.  Hewitt  remarks,  would  be  held  to  be  abomi- 
nable in  this  breed." 

This  is  the  only  record  I  know  of  showing  the  change  that  takes 
place  in  the  Sebright  hen  when  the  influence  of  her  ovary  is  removed. 
There  can  be  no  doubt  from  the  above  description  that  she  changes  in 
the  same  way  as  does  the  castrated  Sebright  male. 

Concerning  the  origin  of  the  Sebright  bantam  Darwin  states  that 
the  race  "originated  about  the  year  1800  from  a  cross  between  a  com- 
mon bantam  and  a  Polish  fowl,  recrossed  by  a  hen- tailed  bantam,  and 
carefully  selected;  hence  there  can  hardly  be  a  doubt  that  the  sickle 
feathers  and  hackles  which  appeared  in  the  old  hen  were  derived  from 
the  Polish  fowl  or  common  bantam;  and  we  thus  see  that  not  only 
certain  masculine  characters  proper  to  the  Sebright  bantam,  but  other 
masculine  characters  derived  from  the  first  progenitors  of  the  breed, 
removed  by  a  period  of  about  60  years,  were  lying  latent  in  this  hen 
bird  ready  to  be  evolved  as  soon  as  her  ovaria  became  diseased." 
To-day  the  problem  appears  to  us  in  a  somewhat  different  light,  since 
the  secondary  sexual  characters  referred  to  by  Darwin  have  simply 
been  kept  under  for  more  than  a  hundred  years  by  the  secretion  pro- 
duced in  the  ovary  of  the  hen  (as  in  all  breeds)  and  in  the  testis  of  the 
male  Sebright. 

HEREDITY  OF  HEN-FEATHERING. 

In  1913  I  found  that  hen-feathering  as  seen  in  the  Sebright  is  a 
dominant  non-sex-linked  character.  A  preliminary  statement  was 
given  in  the  first  edition  of  my  book  on  Heredity  and  Sex  (1913), 
which  treated  the  character  as  a  recessive  one.  This  was  a  mistake 
due  to  a  male  having  been  obtained  that  was  like  the  game  race, 
which  subsequent  work  showed  must  have  been  due  to  a  sperm  hav- 


RELATING    TO    SECONDARY    SEXUAL    CHARACTERS 


15 


ing  been  retained  in  the  oviduct  of  the  female  during  her  isolation 
period.  In  the  second  edition  published  a  few  months  later  the  mis- 
take, having  been  found  out,  was  corrected. 

If  one  dominant  suffices  to  produce  hen-feathering,  the  F2  ratio 
would  be  3  hen-feathered  to  1  cock-feathered  bird.  The  numbers 
found  were  31  to  28.  This  realized  ratio  departs  too  far  from  a  3:  1 
ratio  to  make  it  probable  that  the  results  are  due  to  a  single  factor. 

The  F2  expectation  for  two  dominants,  both  necessarily  present  to 
produce  hen-feathering,  is  9  hen-feathered  to  7  cock-feathered  birds. 
If  the  dominant  factors  are  represented  by  H  and  H'  and  their  wild- 
type  (recessive)  allelomorphs  by  h  and  h',  the  expected  F2  recombina- 
tions are  given  in  the  following  table : 


HH' 

Hh' 

hH' 

hh 

HH'. . . . 
Hh' 

hH'.... 
hh 

/  HH' 
\  HH' 

Hh' 
HH' 

hH' 
HH' 

hh 
HH' 

/  HH' 
\    Hh' 

Hh' 
Hh' 

hH' 
Hh' 

hh 
Hh' 

/  HH' 

\    hH' 

Hh' 
hH' 

hH' 
hH' 

hh 
hH' 

/  HH' 

\     hh 

Hh' 
hh 

hH' 
hh 

hh 
hh 

There  are  9  classes  containing  both  H  and  H',  6  containing  one  or 
the  other,  and  one  containing  neither  H  nor  H\  The  realized  numbers, 
31  to  28,  are  in  close  approximation  to  9:  7. 

In  classifying  the  F2  hen-feathered  males,  an  attempt  was  made  to 
divide  them  into  two  classes,  viz,  type  1,  hen-feathered  to  the  same 
extent  as  the  Sebright,  and  type  2,  intermediate  between  hen  and  cock 
feathering.  The  line  between  intermediate  and  cock-feathering  is 
sharp,  all  the  intermediates  belonging  distinctly  to  the  hen-feat  hered 
group,  but  the  line  between  the  two  subdivisions  of  hen-feathered 
birds  is  not  sharp,  and  occasionally  a  bird  is  found  that  is  difficult  to 
place.  These  statements  hold  also  for  the  Fi  birds,  whose  skins  I  now 
have.  Five  of  these  are  classified  as  intermediates  and  one  as  com- 
pletely hen-feathered.  The  difference  between  these  two  classes,  then, 
is  environmental  or  due  to  other  modifying  genetic  factors,  for  which 
either  the  Sebright  or  the  game  is  not  pure.  Under  these  circumstances 
it  would  not  be  profitable  to  attempt  to  find  out  (without  additional 
evidence)  what  genetic  differences,  if  any,  lie  behind  the  hen-feat  li- 
ered  and  intermediate-feathered  birds  in  the  F2  classes. 

Concerning  the  back-cross  (Fx  by  game)  the  expectation,  for  one 
dominant  factor-difference,  is  1  hen-feathered  to  1  cock-feathered 
male.    There  were  obtained  2  hen-feathered  (intermediates)  to  7  cock- 


16 


THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 


feathered  birds.  The  numbers  are  too  small  to  be  significant,  taken  by 
themselves.  The  expectation  for  2  dominants,  both  essential  to  hen- 
feathering,  is  1  to  3,  and  this  is  in  agreement  with  2  to  7  as  found. 
It  seems,  then,  more  probable  from  the  evidence  of  the  F2  and  of  the 
back-cross  combined  that  there  are  two  dominant  factors  present  in 
the  Sebright  that  make  the  male  hen-feathered,  and  since  the  race 
breeds  true  to  hen-feathering,  both  factors  must  be  present  in  homo- 
zygous condition  unless  an  undetected  lethal  destroys  some  of  the 
classes.1 


Gold  Male 

(Belgian  imported 
from  Brussels.) 


X       Silver  Female 
(Product    of    English 
type  males  for   7 
generations  in  my 
own  yards  ) 


I 
6  Silver  Males 
(Belgian  type) 


6  Gold  Females 


B 


Silver  Cross-Bred  X  Gold  Cross-Bred 


Male 
(offspring  of  A) 


Female 
(offspring  of  A) 


4  Silver  2  Gold 

Males  Males 

(Belgian  (Belgian 

type)  type) 


2  Silver 
Females 


5  Gold 
Females 


Silver  Male 


X        Gold  Female 


6  Silver  Males 
(English  type) 


6  Silver  Females 


D 


Silver  Cross-Bred  X   Silver  Cross-Bred 


Male 
(Offspring  of  C) 


Female 
(Offspring  of  C) 


Silver  Males     Silver  Females    Gold  Females 
(English  type) 


E 


Silver  Male  (offspring  of  C) 


Gold  Female  (pure) 


Silver  Males      Silver  Males      Gold  Males         Gold  Males    Silver  Females    Gold  Females 
(Eng.  type)    (Belgian  type)  (Eng.  Type  1912)  (Belgian  type) 


F 


Silver  Male  (offspring  of  C) 


X 


Silver  Female  (pure) 


Silver  Males  (English  type) 


Silver  Females 


Gold  Females 


Smith  and  Haig  have  reported  the  following  curious  case  of  hen- 
feathering.  Smith  had  a  breed  of  White  Leghorns  with  cocks  of  two 
classes — those  that  assumed  cock  plumage  at  6  months  and  those 
that  are  like  the  hens  for  8  months,  after  which  they  slowly  assumed 
the  cock-feathering.  The  difference  is  hereditary  and  appears  to 
segregate.  Possibly  this  breed  had  one  factor  at  least  for  hen-feathering 
that  is  effective  for  young  birds,  but  not  for  older  ones,  or  some  of  the 

1  The  expectation  for  1  dominant  and  1  recessive  factor  is  so  nearly  the  same  as  for  1  dominant 
alone  that  for  the  numbers  obtained  no  difference  between  the  two  cases  could  be  detected. 


RELATING   TO    SECONDARY    SEXUAL    CHARACTERS.  17 

birds  pass  through  a  stage  when  they  produce  an  internal  secretion 
that  disappears  later.  But  it  is  also  possible,  and  perhaps  more 
probable,  that  the  young  birds,  not  cock-feathered,  have  remained 
longer  in  the  juvenile  stage  than  the  others,  so  that  they  might  be  said 
to  be  falsely  hen-feathered. 

The  results  published  by  the  Rev.  E.  Lewis  Jones  in  1914,  describing 
crosses  between  two  breeds  of  Campines,  one  called  Belgian  (which 
has  hen-feathered  males),  the  other  English  (that  has  cock-feathered 
males),  are  summarized  in  the  table  on  page  16.  They  show  the  domi- 
nance of  hen-feathering  with  some  probability.  The  table  given  there 
is  the  original,  to  which  the  author  has  kindly  added  the  numbers  here 
prefixed  to  some  of  the  classes.  The  numbers  are  not  large  enough  in 
all  cases  to  be  satisfactory,  but  the  dominance  of  the  hen-feathering 
is,  I  think,  apparent,  as  well  as  its  non-sex-linked  transmission.  The 
golden  female  in  C  must  have  been  English  type,  or  at  any  rate  hetero- 
zygous for  English-type  feathering,  for  if  Belgian  her  sons  would  have 
been  Belgian  type. 

Punnett  and  Bailey  (1914)  have  published  the  result  of  a  cross  with 
hen-feathered  Silver  Sebrights  and  Hamburgs.  The  dominance  of 
hen-feathering  in  the  male  is  shown  in  the  figures  that  illustrate  their 
paper,  but  as  the  paper  deals  solely  with  the  inheritance  of  weight  the 
account  of  inheritance  of  hen-feathering  was  deferred  to  a  later  paper, 
that  has  not  yet  appeared. 

HEREDITY  OF  COLOR  IN  THE  CROSS  BETWEEN  SEBRIGHT  AND 
BLACK-BREASTED  GAME  BANTAM. 

The  cross  between  the  Sebright  and  the  Black-Breasted  Game 
bantam  was  undertaken  primarily  to  study  the  inheritance  of  hen- 
feathering.  The  Sebright  was  chosen,  on  the  one  hand,  because  this 
race  is  pure  for  hen-feathering,  whereas  in  other  races,  such  as  the 
Campines,  both  kinds  of  males  are  known.  The  hen-feathered  birds 
of  such  races  are,  I  believe,  frequently  not  pure  for  hen-feathering.  The 
game  race  was  chosen  because  the  cock  has  the  typical  plumage  of  the 
wild  bird,  Gallus  bankiva,  and  although  his  feathers  are  remarkably 
short,  they  show  the  characteristic  cock-feathered  type. 

Only  secondarily  was  the  experiment  concerned  with  color  inheri- 
tance. The  two  breeds  differ  so  markedly  in  coloration  and  pattern 
that  the  very  complex  results  that  appeared  in  F2  were  to  be  expected. 
In  addition  to  the  differences  involving  hen-feathering  versus  cock- 
feathering,  and  Sebright  plumage  versus  game  plumage,  the  game  is 
strongly  dimorphic  in  the  plumage,  while  in  the  Sebright  the  colora- 
tion of  the  two  sexes  is  closely  similar.  But  the  castration  experiments 
have  shown  that  this  difference  is  the  result  of  hen-feathering  in  the 
Sebright  cock,  and  that  the  race  carries  the  same  potential  dimorphism 
as  do  other  races  of  poultry. 


18  THE    GENETIC   AND   THE   OPERATIVE   EVIDENCE 

The  game  cock  is  shown  in  plate  1,  figure  1,  and  plate  4,  figure  1. 
The  wattles  and  comb  had  been  removed  from  the  bird.  The  yellow- 
red  back  and  saddle  are  to  be  noted.  The  upper  tail  coverts  and  sickle 
feathers  are  black,  as  is  the  tail.  These  parts  are  shorter  in  the  game 
than  in  other  races,  being  one  of  the  points  selected  for.  The  dorso- 
anterior  edge  of  the  wing  is  black,  this  color  meeting  across  the  middle 
of  the  back.  Below  this  black  area  comes  the  red  wing  bow,  followed 
by  a  double  row  of  blue-black  feathers.  The  exposed  portions  of  the 
secondaries  are  brown,  of  the  primaries  black  with  green  margin.  The 
breast  and  entire  lower  surface  is  black.  The  legs  are  greenish,  the 
bill  black  and  yellow,  the  iris  yellow. 

The  hen  of  the  Black-Breasted  game  (plate  1,  figure  2)  is  light 
yellowish-brown.  The  back,  saddle,  and  wing  coverts  are  golden 
brown,  finely  penciled  with  darker  brown  or  black.  The  hackle  is 
penciled;  it  has  a  yellow  border  (without  barbules);  the  back  is  more 
brown,  the  forepart  of  the  breast  is  salmon,  the  more  posterior  parts 
lighter  salmon.  The  sides  of  the  body  under  and  below  the  wings  are 
stippled  gray. 

The  Sebright  male  is  represented  in  plate  1,  figure  3.  Photographs 
of  the  male  and  the  female  are  given  in  plate  4  figures  3  and  4.  Most 
of  the  feathers  have  a  yellow  center  and  a  black  border.  Such  feathers 
are  said  to  be  laced.  The  details  of  the  different  regions  are  shown  in 
the  feather  plates,  6  and  8. 

A.  The  Fi  Birds. 

The  Fi  birds  were  remarkably  uniform.  The  sexual  dimorphism 
is  slight,  as  a  comparison  of  the  male  and  female  in  plate  4,  figures  5,  6, 
will  show.  In  the  female  the  body  feathers  are  penciled  but  very 
mossy,  and  this  holds  for  the  male  too,  except  that  in  the  hackle,  back, 
and  saddle,  a  change  in  color  accompanies  the  change  in  shape,  as  seen 
in  the  individual  feathers  in  the  feather  chart  (plate  7,  figure  1).  If 
there  are  any  sex-linked  factors  involved  in  the  cross,  we  should  expect 
different  types  of  Fi  hens  in  the  direct  cross  and  its  reciprocal,  because 
in  one  case  the  Fi  hen  gets  her  single  X  chromosome  from  one  father, 
and  in  the  other  case,  the  reciprocal  cross,  from  the  other.  Unfortu- 
nately no  careful  comparison  can  now  be  made,  because  the  crosses  were 
carried  out  in  different  years  and  the  changes  due  to  age  may  have 
affected  the  color  sufficiently  to  obscure  such  slight  difference  that  may 
have  existed.  But  the  effects  of  such  factors,  if  present,  are  very  small, 
since  the  birds  seemed  to  be  the  same,  regardless  of  the  way  in  which 
the  cross  was  made.  In  the  F2  counts,  although  an  attempt  has  been 
made  to  keep  apart  the  birds  obtained  in  the  two  crosses  {%.  e.,  the  di- 
rect and  the  reciprocal  crosses) ,  it  is  very  doubtful  if  the  two  groups 
show  any  significant  differences. 


RELATING    TO    SECONDARY    SEXUAL    CHARACTERS. 


19 


B.  Description  of  F2  Birds. 

All  together  there  are  72  hens,  29  hen-feathered  males,  and  26  cock- 
feathered  males,  as  shown  in  table  1 : 

Table  1. 


F2  from  Sebright  9  by  Game  cf. 

Fj  from  Sebright  cf  by  Game  9 . 

Females. 

Hen-feath. 
d*  type  1. 

Hen-feath. 
d*  type  2. 

Cock-feath. 

Females. 

Hen-feath. 
<?  type  1. 

Hen-feath. 
d"  type  2. 

Cock-feath. 

A 

B 

C 

D 

E 

F 

G 

H 

I 

J 

K 

L 

M 

N 

O 

P 

15 
1 
3 
3 
6 
6 

11 
5 
1 
2 

3 

2 

1 
5 

4 
2 

1 

4 

1 
1 
2 

1 

1 

2 

1 

1? 

1 

1 

1 
2 
1 

1 
1 

2 
1 

3 
1 

2 

1 

2 
2 
1 

1 
2 

2 
2 
2 

1 

1 

1 

2 

1 
1 

1 

1 

53 

7 

8 

13 

19 

7 

7 

13 

F2  Hens. 

A.  8  females  that  are  like  Fi;  7  others  resemble  them  below,  but  have  stippled  back  and 

rump  feathers  (4  of  these  have  yellow  necks,  and  3  black  necks  like  those  of  Fi). 
Here,  then,  are  two  or  three  subdivisions,  or  perhaps  main  classes. 

B.  1  female  is  very  close  to  game,  having  the  characteristic  stippling  above  and  salmon 

breast  below.     She  is  darker  colored  than  the  game  females,  therefore  more  like 
the  Leghorn  female. 

C.  3  birds  resemble  the  Sebright  in  plumage,  but  would  not  pass  muster  for  real  Sebrights. 

D.  3  others  have  spangled  breast  feathers  like  the  Sebright,  but  a  great  amount  of  stippling 

on  the  back. 

E.  6  birds  are  yellow  on  breast,  with  stippled  back. 

F.  6  others  are  yellow,  stippled  birds  with  a  little  yellow  penciling  on  the  breast. 

G.  11  black  birds  with  some  stippling  on  the  back  of   the  wing,  and   sometimes  with 

traces  of  yellow  in  the  hackle. 

H.  6  other  birds  are  dark,  but  not  as  black  as  the  last.  There  is  some  stippling,  especiallv 
on  breast.  The  hackle  is  always  striped.  (4  of  these  have  yellow  necks  above 
and  below;  2  have  dark  necks.)  The  series  of  feathers  photographed  in  plate  10, 
figure  4,  from  a  bird  of  class  H,  show  all  gradations  between  a  spangled  and  a 
barred  condition.  It  is  practically  certain  that  the  barring  seen  here  (as  well  as 
that  under  class  M)  is  quite  different  from  that  of  the  Barred  Plymouth  Rock. 

7.  1  yellow  hen  with  a  little  black  (as  a  band)  on  wings  and  tail. 

J.  2  other  yellow  birds  with  a  little  black  penciling  on  the  back,  the  tail,  and  with  long 
wing  feathers. 

Fj  Males. 

K.  2  intermediate  males  with  a  black-splotched  red  breast  and  black  tail.  The  saddle  is 
coarsely  stippled.     The  corresponding  male-feathered  bird  is  red  above. 

L.  A  Sebright-like  bird  with  black  stippled  feathers  on  back;  the  rest  of  the  plumage 
heavily  laced.     Posterior  part  of  breast  and  thigh  black.     The  tail  stippled. 


20  THE    GENETIC    AND    THE    OPERATIVE    EVIDENCE 

M.  Yellow  neck,  the  back,  tail,  and  lower  half  of  each  secondary  coarsely  stippled.  Pos- 
terior part  of  breast  barred;  cape  and  anterior  breast  penciled.  The  series  of 
feathers  photographed  in  plate  10,  figure  5,  from  the  breast  of  a  bird  in  class  M, 
shows  all  possible  gradations  from  a  penciled  to  a  barred  condition. 

0.  1  cock-feathered,  Red-Breasted  game  with  somewhat  stippled  feathers.  The  lower  half 
of  each  secondary  is  penciled  (Hamburg  type). 

P.  1  intermediate  male  with  yellow  hackle  that  is  black  striped.  He  has  a  peculiar  saddle, 
the  general  color  of  which  is  reddish  brown.  Each  feather  has  a  faint  black  edge, 
and  is  clear  yellow  along  shaft;  the  rest  of  the  feather  is  finely  dusted  on  a  yellow 
background  (plate  10,  fig.  3).  Breast  feathers  (in  front  part)  are  laced  with 
an  outer  black  band  edged  with  yellow.  In  the  posterior  region  of  the  breast  the 
feathers  are  broadly  laced.  Wing-bow  and  coverts  red,  laced  with  black.  The 
exposed  edges  of  primaries  and  secondaries  are  red-brown,  the  covered  parts  black. 
The  tail  is  black. 

Back-Cross  Hens. 

A.  Two  dark  Fi  types.     The  breast  is  between  stippled  and  penciled,  the  head  is  black. 
C.  (1)  Sebright  type.     Very  dark  with  much  stippling.     Some  penciling  on  back.     Breast 
dark;  neck  like  that  of  Sebright. 

(2)  Sebright  type  like  (1),  but  not  such  clear  yellow.     Secondaries  and  tail  feathers 

and  coverts  stippled  (with  black  tips). 

(3)  Yellow  Sebright.     Neck  and  breast  yellow  with  black  base  and  tip  to  feathers. 

Cape,  breast,  and  wings  (except  bow)  penciled  to  barred. 
C.  to  D.  (1)  Pale  yellow,  breast  spangled,  back  lightly  penciled,  tail  same.     Secondaries 
yellow  and  little  stippled.     Upper  web  of  primaries  stippled. 

(2)  Breast  spangled,  rest  as  in  (1). 

(3)  Same  as  (2). 

L.  Dark  Sebright.  Back-feathers  broadly  laced  and  a  little  penciled.  Neck  black  with 
yellow  centers  to  feathers  and  yellow  edges  (reversed  Sebright). 

All  of  the  preceding  hens  except  A  are  in  general  Sebrights.  The 
last  three  are  pale  stippled  Sebrights. 

Back-Cross  Hen-Feathered  Cocks. 

A.  One  cock  like  Fi  male,  but  rather  paler  on  back. 

C.  Four  cocks.     Light  Sebrights,  but  spangled,  in  general,  instead  of  laced.     Feathers 

clear,  not  stippled. 
G.  One  black. 

L.  Dark  Sebright.     Back  and  rump  black.     Feathers  with  narrow  center,  not  stippled. 
Q.  Dark  Sebright  nearer  to  hen  C  (1).     Thoroughly  stippled  with  game  tail.     Neck  and 

breast  dark  Sebright.     Probably  a  new  class  nearer  to  (C). 
R.  Two  cocks.     Pale  yellow  instead  of  reddish,  and  much  less  black  than  are  other  yellows. 

No  class  of  hens  to  match.1 

In  regard  to  color  inheritance  the  preceding  19  birds  are  too  few 
to  add  anything  of  significance  to  the  other  results,  except  that  they 
serve  to  emphasize  the  dominance  of  the  factors  making  for  Sebright 
coloration.  The  hen-feathered  cocks  confirm  the  other  results  as  to 
the  dominance  of  the  factor  or  factors  in  question. 

There  can  be  little  doubt  that  some  of  these  classes  are  complex. 
They  almost  merge  into  each  other  and  in  one  part  of  the  body  individ- 

1  There  is  one  other  bird,  not  given  in  the  above  list,  that  is  pure  Sebright  except  that  his  legs 
are  yellow.  Until  I  find  out  by  further  breeding  of  the  Sebright  stock  whether  yellow  legs  are 
present  in  it,  this  case  must  remain  doubtful.  On  the  basis  of  a  two  factor  color-difference  one 
Sebright  (as  to  color)  is  expected  in  16  birds,  and  one  in  64  on  a  three  factor  basis.  Some 
Sebrights  had  been  raised  along  with  the  back  cross,  hence  the  possibility  of  contamination. 


RELATING   TO    SECONDARY    SEXUAL    CHARACTERS.  21 

uals  may  grade  off  into  one  class,  in  other  parts  into  other  classes. 
An  almost  continuous  series  of  types  might  be  arranged  from  black 
to  pale  yellow. 

The  difficulty  of  matching  the  hen-feathered  males  to  their  genetic 
mates  is  almost  insuperable.  In  table  1  an  attempt  was  made  to  put 
these  males  with  their  respective  females.  The  difficulty  is,  of  course, 
greater  for  the  cock-feathered  birds,  even  with  the  castration  evidence 
(that  is  too  meager  at  present  for  the  purpose) ,  but  a  few  of  the  males 
may  be  placed  with  certainty,  and  the  rest  guessed  at. 

One  bird  appears  to  be  a  hen-feathered  game  male  resembling  in 
many  respects  the  female  game,  but  darker  and  redder.  There  is  more 
shafting  on  cape  and  wing-bow.  The  breast  is  unusually  dark-salmon. 
The  hackle  is  darker  than  is  the  game  female.  Upper  wing-coverts 
broadly  laced  with  black.    (Plate  10,  fig.  3.) 

The  occurrence  of  this  hen-feathered  jungle-fowl  is  so  unique  and 
the  coloration  of  the  bird  so  interesting  that  I  have  added  to  the  plates 
three  feathers  of  such  a  bird,  viz.,  a  stippled  saddle  feather,  a  feather 
from  the  back,  a  hackle  feather,  and  a  wing  covert  with  stippled  center 
and  a  black  border.  The  neck  hackle  departs  somewhat  from  the 
hackle  of  the  jungle-fowl  hen,  but  in  the  same  direction  as  does  the 
neck  hackle  of  the  Sebright  cock  from  his  hen. 

Looking  over  the  F2  group,  the  most  noticeable  thing  is  the  large 
number  of  blacks  (E  and  G),  all  of  which  are  stippled.  Probably  the 
factor  came  from  the  game,  because  group  E  was  present  in  the  back- 
cross  as  well  as  in  F2,  and  because  these  black  birds  are  always  stippled. 
The  yellow  color  (land  J)  may  have  come  from  both,  each  breed  having 
then  a  black  factor  that,  as  a  pattern,  covers  over  most  of  the  yellow. 
It  is  difficult  to  distinguish  penciling  from  stippling  in  the  F2  yellows. 
Without  figuring  each  of  these  types,  their  description  in  detail  is  not  of 
much  value.  The  skins  will  be  deposited  for  reference  in  the  Zoological 
Laboratory  of  Columbia  University. 

C.  Back-Cross  of  Fj  to  Game. 

As  the  back-cross  of  the  Fj  to  the  game  might  appear  more  likely  to 
reveal  the  kinds  of  germ-cells  present  in  the  individual,  the  results 
from  such  a  cross  may  be  given  before  discussing  the  genetic  data.  If 
it  were  certain  that  the  "game"  contained  all  of  the  recessive  factors 
that  are  involved  in  the  experiment,  this  method  of  testing  the  result 
would  be  ideal,  but  there  is  no  way  of  determining  a  priori  whether 
this  is  the  case.  The  question  will  be  taken  up  later.  The  pre- 
sence of  two  kinds  of  males  with  corresponding  but  largely  uncor- 
related  differences  in  their  plumage  makes  their  classification  as  a 
group  impossible.  It  is  simpler,  therefore,  to  put  the  females  into  their 
classes  first,  after  which  the  hen-feathered  males  may  be  expected  to 
fall  into  the  same  groups  (or  nearly  so),  while  the  identity  of  the  cock- 


22 


THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 


feathered  males,  i.  e.,  their  class  relationship  can  only  be  determined 
for  the  classes  that  resemble  the  Fx  and  the  Pi  birds.  The  F2  hen- 
feathered  males  can  in  part  be  further  identified  by  means  of  the 
evidence  that  castration  of  these  types  affords. 

Two  of  the  F2  classes  of  hens  can  be  identified  in  this  back-cross, 
viz,  (a)  4  hens  like  the  Fi  birds,  (6)  3  hens  like  the  game;  (c)  there  were 
3  other  hens  with  plain  yellow,  i.  e.,  not  stippled  backs.  The  upper 
surface  was  like  that  of  the  game  female,  but  much  lighter.  The  first 
two  classes  (a),  (b)  might  be  again  split  into  two  types.  There  were 
only  two  hen-feathered  males,  one  nearly  like  the  Fi  male,  the  other 
blacker;  they  probably  belong  to  different  classes. 

Of  the  7  cock-feathered  males,  one  was  like  the  Fi  castrated  males; 
another  had  a  similar  back,  but  a  darker  and  differently  marked 
breast;  2  were  game-cock  type;  3  were  odd  birds  much  like  the  game 
cock  above  except  for  absence  of  black,  with  reddish  heads  without  any 
black.    The  males  may  be  approximately  classified  as  follows : 


Back-cross  Fi  9  by  game  cf. 

Hen-feath- 
ered cf. 

Interme- 
diate d1- 

Cock-feath- 
ered cT. 

F  (or  K) . . 

1 
1 

1 
2 
2 
2 

(C) 

B 

A 

7 

Four  or  five  types  may  then  be  recognized  in  this  rough  grouping. 
None  of  the  groups  seem  uniform  and  probably  might  be  split  again. 


D.  The  Number  of  Color  Factors  Involved. 

The  theoretical  expectation  for  two  pairs  of  factors  calls  for  4  classes 
in  the  back-cross,  but  this  assumes  that  the  parent  type  used  for  back- 
crossing  contains  all  (here  2)  recessives.  But  this  simple  assumption 
can  not  be  true  in  this  case,  for  the  Fx  bird  would  have  been  like  the 
Sebright.  On  the  3-factor  assumption  the  expectation  for  the  back- 
cross  is  8  classes,  but  this  would  apply  only  if  the  game  were  the  triple- 
recessive  form,  which,  again,  it  is  not,  as  shown  by  the  F]  cross.  But  if 
the  dominance  of  one  or  more  of  the  Sebright  color  factors  is  incomplete, 
then  either  a  2  or  3  factor  assumption  might  apply  to  the  back-cross. 

If  only  2  pairs  of  factors  are  present  we  should  expect  to  recover  the 
game  type  once  in  16  cases  in  F2.  But,  as  will  be  shown,  only  1  game 
was  recovered  out  of  the  49  F2  females.  This  result  fits  better  with  a 
3-factor  assumption,  for  even  with  the  small  number  in  the  back-cross 
the  indications  are  that  more  than  4  classes  are  present. 


RELATING   TO    SECONDARY   SEXUAL   CHARACTERS.  23 

In  the  F2  birds  at  least  11  classes  may  be  distinguished,  and  some 
of  these  appear  composite.  For  3  factors  the  maximum  number  of 
possible  classes  (including  heterozygotes)  is  27.  We  can  recognize  at 
least  11  F2  classes  amongst  the  females  alone,  and  a  few  others  are 
doubtfully  present  in  the  males. 

In  favor  of  the  view  that  the  heterozygous  classes  are  here  different 
from  the  homozygous,  the  following  evidence  may  be  utilized : 

(1)  The  Fx  birds  are  entirely  different  from  either  parent  and  they 
are  heterozygous  for  all  the  factor  differences  between  the  two  types. 
The  only  alternative  explanation  for  the  intermediate  condition  of  Fi 
would  be  that  each  race  carries  one  or  more  completely  dominant 
factors.  But  the  latter  view  is  improbable  because  more  of  each  parent 
type  would  then  be  expected  in  the  F2  generation. 

(2)  In  the  F2  generation  the  Fx  type  is  not  as  frequent  as  would  be 
expected  on  the  view  that  the  heterozygotes  could  not  be  distinguished. 

E.   Back-Cross  of  Fx  9  to  Sebright  cf. 

It  is  possible  to  add,  now,  while  this  paper  is  passing  through  the  press 
(June  1919),  the  results  of  a  back-cross  of  4  Fi  females  to  a  Sebright 
male  carried  out  during  the  summer  of  1918.  The  birds  being  now 
mature  their  permanent  colors  are  evident.  Making  the  back-cross 
in  this  direction  is  much  less  advantageous  than  the  reciprocal  de- 
scribed above,  because  the  Sebright  contains  most  of  the  dominant 
color  factors.  The  group  of  birds  obtained  appeared  to  be  less  varia- 
ble in  color  than  those  from  the  other  back-cross,  and  one  can  see  at  a 
glance  that  more  of  them  approach  the  Sebright  type;  some  quite 
closely. 

All  of  the  males  are  hen  feathered,  as  expected.  No  evidence  was 
found  that  two  types  of  males  exist,  which  would  have  been  expected 
if  the  two  types  noted  in  F2  had  any  hereditary  significance.  If,  then, 
as  the  F2  results  suggest,  two  factors  for  hen-feathering  are  present 
both  are  dominant,  and  no  genetic  distinction  is  found  between  in- 
dividuals in  which  one  or  both  of  the  dominaut  factors  are  duplex 
or  simplex. 

There  were  9  adult  hens  and  10  hen-feathered  cocks.  An  attempt 
is  made  below  to  refer  them  to  their  corresponding  F2  classes. 

F.  Review  of  the  Heredity  of  the  Color  of  the  Plumage  of 

Poultry. 

In  poultry  there  are  perhaps  more  different  colors  and  color-patterns 
than  in  any  other  species  of  domesticated  animals.  The  genetic  work 
has  advanced  far  enough  to  show  that  many  of  the  differences  depend 
on  Mendelian  factors.  It  is  probable  that,  in  addition  to  the  main 
factors,  there  are  many  contributory,  minor,  or  modifying  factors  that 
give  the  finer  details  to  "show  birds." 


24       THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

It  is  generally  supposed  that  the  wild  bird  from  which  some  at  least 
of  the  domesticated  races  have  come  is  Gallus  bankiva  of  India  and 
Indo-China,  or  else  one  or  another  of  its  subspecies.  In  any  case, 
the  wild  type  of  coloration  is  approximately  known,  since  the  known 
wild  races  are  colored  alike  in  all  essential  respects.  Even  were  the 
color  of  the  wild  type  not  known,  the  original  plumage  could  be 
deduced  with  some  degree  of  probability  from  the  atavism  that 
appears  when  some  of  the  races  are  hybridized.  It  is  interesting  to  find 
that  many  of  the  new  plumage  characters  are  dominant  to  the  wild 
type.  The  same  relation  also  holds  rather  generally  for  other  characters 
of  poultry,  such  as  the  comb,  etc. 

Amongst  the  uniform  or  single-colored  races,  the  whites,  blacks, 
reds,  and  buffs  have  been  studied.  Bateson  and  Punnett  were  the  first 
to  show  that  the  white  of  the  White  Leghorn  is  dominant.  They  also 
showed  that  the  white  of  the  White  Rose  Comb  bantams  is  recessive. 
Another  white,  that  of  the  White  Silky,  is  also  recessive,  but  due  to  a 
different  factor  from  the  white  factor  of  the  Rose  Comb  bantams;  for, 
when  these  two  whites  are  bred  together  they  give  colored  birds  in  the 
first  generation.  Hurst  showed  later  that  the  white  of  the  Leghorn 
is  dominant  over  the  black  of  the  Hamburg  and  the  buff  of  the  Cochin. 
The  dominance  is  often  not  complete,  since  tints  of  black  or  of  buff  or 
even  patches  of  these  colors  may  occur.  The  latter  may  be  confined 
to  the  head,  neck,  and  breast.  The  black  plumage  of  the  Hamburg  is 
dominant  over  the  buff  of  the  Cochins,  but  incompletely  so,  as  the 
black  background  may  be  marked  and  shaded  with  brown.  Whether 
we  are  dealing  here  with  one  pair  of  factors,  or  two  pairs,  could  only 
be  determined  by  an  F2  ratio;  whether  it  is  3:  1  or  9:  3:  3:  1. 

The  blue  color  of  the  Andalusian  is  known  not  to  be  a  simple  color, 
but  to  be  a  fine  mosaic  of  splashed  white  and  black.  The  color  is 
produced  in  birds  that  are  heterozygous  for  splashed  white  and  black, 
or  at  least  for  certain  kinds  of  white  and  black.  This  relation  was  first 
demonstrated  by  Bateson  and  Punnett  (1902  and  1905)  and  later 
Saunders  (1906).  It  appears  also  from  certain  crosses  made  by  Daven- 
port that  some  of  the  whites  (such  as  that  of  the  Leghorn)  and  black 
(such  as  that  of  the  Minorca)  may  at  times  also  give  some  blue  birds 
when  crossed.  Whether  there  are  also  other  races  with  dominant 
white  color  different  from  that  of  the  Andalusian  white  (and  the  same 
holds  for  black  races  also)  or  whether  a  special  (recessive)  white  was 
present  in  this  cross  when  the  blue  appeared,  was  not  made  out  by 
Davenport. 

Lippincott  has  recently  studied  the  Andalusian  cross  and  obtained 
essentially  the  same  results  as  his  predecessors.  He  calls  attention  to 
an  interesting  fact  in  the  splashed  whites,  namely,  that  the  color 
splashes  are  blue  when  thay  are  found  in  those  parts  of  the  body  where 
the  color  is  blue  in  the  Andalusian.    Although  the  Andalusian  is  always 


RELATING   TO    SECONDARY    SEXUAL    CHARACTERS  25 

spoken  of  as  a  blue  bird,  the  hen  only  is  entirely  blue,  while  the  male  is 
black  above  and  blue  below.  The  splashes  on  a  white  male  correspond 
to  the  black  and  blue  of  the  Andalusian  male,  and  are  black  if  above 
and  blue  if  below. 

Lippincott  found  also  that  the  blue  birds  differ  from  the  black  in  two 
characteristics,  viz,  in  the  blues  the  pigment  is  in  larger  masses,  i.  e., 
it  is  more  clumped,  leaving  more  white  between  the  clumps  than  in 
the  blacks,  and  in  the  blues  the  pigment  is  absent  in  the  extremities 
of  the  barbules.  If  the  clumping  and  the  condition  of  the  barbules  are 
treated  as  separate  entities,  each  gives  a  3:  1  ratio.  Lippincott  con- 
cludes, therefore,  that  the  Andalusian  cross  is  a  2-factor  case.  If  each 
of  these  characteristics  was  independent  of  the  other  in  the  sense  that 
some  birds  had  clumped  pigment  and  others  deficiencies  in  the  barbules, 
then  one  might  conclude  that  he  was  dealing  with  a  2-factor  case;  but 
if  these  two  characters  are  only  different  aspects  of  the  same  gene,  and 
when  one  is  present  the  other  is  also,  the  situation  is  not  different  from 
those  that  are  very  common,  viz,  two  or  more  effects  produced  by  the 
same  genetic  factor. 

Davenport  has  recorded  results  of  crossing  several  breeds  of  different 
colors  (1906  and  1909).  The  white  of  the  Leghorn  was  found  dominant 
to  the  black  of  the  Minorca  breed,  although  the  hybrids,  "at  least  the 
females,"  had  some  black  feathers.  This  white  was  also  found  to  be 
dominant  to  the  mottled  Houdan  and  to  the  "Red-backed  game." 
On  the  other  hand,  a  male  Tosa  with  wild-type  plumage  by  recessive 
White  Cochin  female  gave  "  barred  "  males  in  Fij  the  barring  coming 
in,  no  doubt,  from  the  Cochin  and  although  not  at  the  time  recognized 
by  Davenport  as  sex-linked  inheritance,  the  statement  that  barring 
is  "associated  with  maleness"  (as  already  pointed  out  by  Darwin) 
indicated  that  the  barring  that  appeared  within  the  cross  was  probaUy 
the  sex-linked  barring  shown  by  other  breeds. 

In  Davenport's  cross  of  White  Leghorn  by  Minorca  two  bines 
appeared  (as  stated  above),  indicating  that  the  same  factors  were 
here  present  that  in  the  Andulusian  white  and  black  strain  gives  the 
same  result,1  but  why  only  some  of  the  Fi  appear  as  blue,  while  others 
are  not  blue,  is  not  yet  made  clear,  unless  two  factors  for  white  were 
present.  White  of  the  Leghorn  breed  was  found  not  to  be  as  com- 
pletely dominant  over  buff  as  over  black.  Black  was  found  dominant 
over  the  wild-type  (Black-Breasted  game),  but  red  is  present  in  1  ■". 
birds  also  to  some  extent  in  those  places  where  red  is  found  in  the  game. 
Lacing,  as  shown  by  the  Dark  Brahma,  is  dominant  to  the  plumage 
of  the  Tosa.  Penciling  also  is  said  to  be  dominant,  as  shown  in  females 
of  the  cross  between  the  Dark  Brahma  and  Tosa  fowl. 

In  his  later  paper  (1909)  Davenport  gives  fuller  information  in 
regard  to  some  of  the  Fx  cases  reported  in  his  first  paper,  as  well  as  the 

1  Provided  that  the  blue  classification  was  based  on  the  adult  plumage  and  not  on  down  r,.\nr. 


D.  H.  HILL  LIBRARY 
Norfh  Carolina  State  College 


26  THE    GENETIC   AND   THE    OPERATIVE   EVIDENCE 

F2  results.  Thus,  in  the  cross  of  Silky  to  Minorca,  that  gives  black 
Fi  birds,  the  F2  count  gave  210  black,  57  game,  and  95  white — approxi- 
mately the  expectation  for  two  pairs  of  factors,  one  of  them  giving 
white  (9:3:4).  Silky  by  White  Leghorn  gave  white  Fi's,  but  the  males 
developed  red  on  the  wing  bow  and  saddle  when  they  became  mature, 
and  the  female  a  faint  blush  of  salmon  ("red")  on  the  breast.  In  F2 
there  were  whites,  games,  and  blacks,  approximating  to  expectation  for 
three  pairs  of  factors,  one  being  a  dominant  white  (52:  9:3).  Silky 
by  Buff  Cochin  gave  a  washed-out  buff,  but  with  the  jungle  coloration 
partly  developed  in  the  tail  (black)  and  hackles  and  wing  bow  (redder 
buff).  Davenport  represents  the  Buff  Cochin  as  having  lost  the  jungle 
patterns  and  coloration,  while  the  Silky  retains  it.  The  heterozygous 
condition  of  the  genes  for  the  wild-type  color  in  Fi  is  made  responsible 
for  the  part  development  of  color.  The  White  Silky  is  represented  as 
carrying  the  factor  for  black  (N),  hence  in  F2  both  black  and  game- 
colored  birds  are  expected  and  they  were  obtained.  When  Black 
Cochin  is  crossed  to  Buff  Cochin,  the  Fx  males  are  in  general  like  the 
game  (black  and  red)  while  the  females  are  black  (except  for  some  red 
on  the  hackle).  In  this  case  Davenport  represents  the  Black  Cochin  as 
showing  a  factor  for  jungle-fowl  pattern,  but  lacking  the  color  that  is 
assumed  in  his  other  formulae  to  go  with  this  pattern.  What  is  meant 
by  this  change  is  not  quite  clear  to  me,  unless  Davenport  supposes  there 
is  an  independent  factor  for  the  jungle-fowl  pattern  which  may  be 
filled  in  by  other  colors  determined  by  other  factors.  But  were  there 
enough  Fi  birds  to  exclude  the  possibility  that  jungle-fowl  birds  would 
not  appear  in  this  cross? 

Davenport  has  reported  a  cross  between  a  female  White  Cochin  and 
a  male  Tosa  (wild  type)  from  which  the  daughters  were  Tosa,  except 
that  the  shafting  was  broadened,  and  the  saddle  feathers  and  proximal 
secondaries  were  obscurely  barred  (black  and  buff) ;  the  sons  were  also 
like  the  Tosa,  but  every  feather  was  repeatedly  barred  (see  above). 
In  F2  there  were  15  white,  25  game,  and  16  barred  birds.  Davenport 
concludes  that  "barring  is  clearly  heterozygous  and  confined  to  the 
male  sex,"  and  in  a  footnote  he  adds  that  the  sex-linked  barring  factor 
of  the  Plymouth  Rock  is  different  from  that  of  this  Cochin-Tosa  cross, 
but  Goodale  informs  me  that  the  barring  that  appeared  in  this  cross 
is  probably  the  same  as  that  in  Barred  Rocks. 

As  pointed  out,  an  interesting  feature  of  color  inheritance  in  poultry 
is  the  large  number  of  cases  of  sex-linked  inheritance.  It  might  seem 
probable  here,  as  in  the  case  of  Drosophila,  that  this  is  due  to  a  well- 
recognized  difference  between  sex-linked  and  autosomal  characters, 
namely,  that  a  recessive  mutation  in  one  of  the  sex  chromosomes  of  a 
sperm-cell  of  the  male  bird  will  have  a  chance  of  showing  its  effect 
immediately  if  that  sperm-cell  unites  with  an  egg  without  a  Z  to  form 
a  daughter,  whereas  it  would  not  immediately  show  up  in  the  offspring 


RELATING   TO   SECONDARY   SEXUAL   CHARACTERS.  27 

if  the  mutation  were  autosomal.1  In  consequence  the  recessive  mutant 
would  have  a  greater  chance  of  being  observed  and  selected  if  it 
appeared  in  a  sex  chromosome.  But  dominant  sex-linked  characters, 
however,  have  the  same  chance  as  dominant  autosomal  ones  and  the 
question  turns  therefore  on  the  kinds  of  characters  shown  in  the  cross. 

The  first  indication  of  sex-linkage  in  fowls  was  furnished  by  evidence 
that  Spillman  published  in  1903  on  information  supplied  by  poultry- 
men — information  that  has  been  proven  subsequently  to  have  been 
accurate.  Spillman  pointed  out  clearly  the  similarity  between  the 
facts  he  quoted  and  the  then  known  cases  of  sex-linkage  in  the  canary 
and  in  the  currant  moth.  The  case  referred  to  by  Spillman  was  a  cross 
between  Barred  Plymouth  Rock  and  Black  Langshan.  Goodale  and 
I  repeated  the  cross,  using  both  Plymouth  Rock  and  American  Dom- 
inques,  publishing  the  results  in  1912.  In  addition  to  the  Fi  results 
evidence  was  obtained  for  the  F2  generation.  The  theory  was  also 
tested  by  back-crossing.  The  results  of  such  a  cross  that  are  typical 
for  all  cases  of  the  sort  are  briefly  as  follows :  Plymouth  Rock  cock  by 
Langshan  hen  gives  Fi  barred  sons  and  barred  daughters.  These 
inbred  give  F2  barred  cocks  and  barred  and  black  hens  (2:1:1). 

In  the  following  schemes  the  sex  chromosomes  are  represented  by  Z 
and  W,  while  the  exponents  stand  for  the  factors  involved,  viz,  B  for 
barred  and  b  for  not-barred,  which  here  means  a  black  bird. 

Barred  $  Black  9 

?i  zBzB  zV 


zBzb     zV 

F>  BarredcT      Barred  j 


-ft    -ft    zV      zV 

Barredc?   Barredd*     Barredj      Blacky 

In  the  reciprocal  cross,  a  black  cock  was  mated  to  a  barred  hen. 
The  sons  were  barred,  the  daughters  black  (F,).  These  inbred  gave 
(F2)  barred  males  and  females,  black  males  and  females  in  the  ratio 
of  1:1:1:1.    The  chromosome  scheme  of  inheritance  is  as  follows: 


B&ckd" 


n 


zV      zV 

1  Barred^"       Black  j 


zBzb  z*zb     zV    z\v 

Barredc?    Black  c?       Barred<j>     Black  j 


1  If  the  recessive  mutation  occurs  first  in  the  Z  chromosome  of  an  egg  of  the  female  it  will  not 
appear  in  the  next  generation;  then  if  it  has  passed  into  a  male,  half  hi.s  daughters  will  show  it. 
The  single  factor-pair  involved  is  carried  by  the  sex  chromosomes  Z  Z. 


28  THE    GENETIC    AND    THE    OPERATIVE    EVIDENCE 

One  back-cross  test  consists  in  mating  the  Fx  barred  males  ZBZb 
(from  both  crosses)  to  a  pure  black  female.  The  expectation  is  for 
equal  numbers  of  barred  and  black  males  and  females,  and  the  result 
was  realized.  The  Fx  barred  hen  of  the  first  cross  (ZBW)  back-crossed 
to  a  black  cock  is  expected  to  give  only  barred  males  and  black  females, 
and  this  result  also  was  obtained.  The  explanation  of  the  last  cross, 
based  on  the  sex  chromosomes,  is  as  follows : 

Sack  <?  £  Barredj 


Before  these  experiments  were  finished  Goodale  had  made  other 
crosses  involving  the  barring  factor,  and  had  obtained  results  that 
showed  the  sex-linked  inheritance  of  this  factor  (1909).  For  example, 
he  crossed  Buff  Rock  male  (not  barred)  to  white  Plymouth  Rock 
females.  The  sons  were  barred  and  the  daughters  not  barred.  The  re- 
ciprocal cross  gave  barred  sons  and  daughters.  A  White  Rock  male 
(carrying  barring)  mated  to  a  Brown  Leghorn  female  gave  barred  sons 
and  daughters.  Reciprocally,  the  chicks  were  of  two  kinds  as  to  their 
down,  viz,  black  chicks  and  chicks  with  the  down  pattern  of  the  barred 
rock.  All  these  results  with  Barred  Plymouth  Rocks  show  that  they 
carry  a  sex-linked  dominant  factor  for  barring.  Its  wild-type  allelo- 
morph would  be  game-color  (jungle-fowl),  but  since,  when  the  dominant 
barring  is  absent  in  some  of  the  individuals  in  these  crosses,  they  are 
black,  it  would  seem  to  follow  that  another  dominant  factor,  one  for 
black,  that  is  not  sex-linked,  is  also  present. 

Pearl  and  Surface  have  also  carried  out  crosses  with  Plymouth 
Rocks  on  a  much  larger  scale.  Their  results  conformed  in  every  way 
to  the  foregoing.  They  crossed  Barred  Plymouth  Rocks  and  Cornish 
Indian  games.  The  plumage  of  the  male  of  the  latter  race  is  black 
with  dark  red  on  the  back  and  wing-bows;  the  females  are  also  black 
laced  with  mahogany  ground-color  on  back,  breast,  wing,  and  tail 
coverts.  When  the  male  game  is  mated  to  the  barred  hen  the  sons  are 
barred  and  the  daughters  are  black.  In  the  reciprocal  cross  both  sons 
and  daughters  are  barred.  The  back-cross  tests  conformed  to  expecta- 
tion. The  results  were  the  same  as  those  already  stated  above  for  the 
Langshan-Rock  cross. 

Sturtevant  crossed  Columbian  Wyandottes  and  Brown  Leghorns. 
The  Fi  sons  were  alike,  whichever  way  the  cross  was  made.  They  were 
fairly  typical  Wyandottes,  which  race  carries  therefore  more  of  the 
dominant  plumage  characters  (two  or  three?).  There  were  two  types 
of  daughters,  depending  on  the  direction  in  which  the  cross  was  made. 


RELATING    TO    SECONDARY    SEXUAL    CHARACTER-.  29 

When  the  father  is  Wyandotte,  the  daughters  are  like  him  (except  for 
stippling  of  the  Leghorn  type).  When  the  father  is  Brown  Leghorn 
the  daughters  are  somewhat  stippled  red  birds.  In  the  former  case 
the  daughters  getting  their  Z  chromosome  from  their  Wyandotte 
father  resemble  him;  in  the  latter  case  the  daughters  getting  their  Z 
chromosome  from  their  Leghorn  father  look  more  like  him.  Their 
failure  to  look  exactly  like  him  must  be  due  to  autosomal  factors 
derived  from  the  Wyandotte  mother  that  dominate  other  autosomal 
factors  from  the  father. 

Hagedoorn  crossed  Black  Breasted  Game  bantams  (like  those  used 
in  my  Sebright  crosses)  to  Brown-Breasted  bantams.  In  the  latter 
the  black  breast  feathers  of  the  male  are  bordered  bjr  lemon ;  the  hens 
are  nearly  black.  Black-breasted  male  to  ''brown-red"  female  gave 
both  black-breasted  sons  and  daughters.  In  the  reciprocal  cross  all 
the  sons  were  black-breasted  (like  the  mother)  and  all  the  daughters 
were  brown  red  like  the  father.  Evidently  the  factor  here  for  Brown 
Breasted  game  is  sex-linked  and  recessive.  In  this  case  the  new 
mutant  sex-linked  character  is  recessive  to  the  wild  type. 

Davenport  (1912)  crossed  Brown  Leghorns  to  Dark  Brahmas.  In 
the  cross  and  its  reciprocal  all  the  sons  are  alike.  Two  dominant  sex- 
linked  factors  were  found,1  viz,  the  white  background  characteristic  of 
the  Dark  Brahmas  and  the  red  upper  wing-coverts  (and  back)  charac- 
teristic of  the  Brown  Leghorns.  On  the  other  hand,  the  daughters 
differ  in  the  two  crosses,  in  each  case  resembling  their  father  in  their 
hackle  color. 

When  two  sex-linked  characters  are  involved  in  a  cross  it  is  possible 
to  determine  by  suitable  matings  whether  an  interchange  between  the 
chromosomes  that  bear  them  has  taken  place.  In  the  case  of  the  sex 
chromosomes  only  one  sex,  the  male,  has  both  like  chromosomes,  viz, 
ZZ,  and  we  expect  from  analogy  with  the  Drosophila  work  that 
crossing-over  would  be  found  between  the  sex  chromosomes  only  in 
the  male.  Goodale  has  recently  (1917)  made  the  important  discovery 
that  in  poultry  crossing-over  takes  place  between  the  sex  chromosomes 
(ZZ)  in  the  male,  but  not  in  the  female  (ZW  or  ZO).  This  relation, 
therefore,  is  the  reverse  in  birds  and  flies,  for,  in  the  one,  crossing- 
over  takes  place  in  the  female  and  in  the  other  in  the  male.  Whether 
this  difference  extends  also  to  the  other  chromosomes  in  birds  as  it 
does  in  flies  is  as  yet  not  known. 

Several  years  ago  some  crosses  between  gold  and  silver  Campinee 
were  reported  by  Rev.  E.  Lewis  Jones.  The  results  are  consistent  with 
the  view  that  a  sex-linked  factor  pair  is  responsible  for  this  difference 
in  color,  although  the  author  does  not  apply  this  view  to  his  results. 
The  results  may  be  seen  in  the  table  on  page  16,  to  which  Jones  has 

1  One  may  be  either  sex-linked  or  sex-limited  so  far  as  the  evidence  gOW. 


30       THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

prefixed  the  number  of  individuals.  The  cross  also  involved  hen- 
feathering  versus  cock-feathering,  which  appears  here  (as  in  other 
cases)  to  be  a  non-sex-linked  dominant  factor.  As  stated  above  there 
are  in  the  results  a  few  apparent  inconsistencies  with  this  interpre- 
tation, due  possibly  to  heterozygous  females  having  been  used  in  the 
crosses. 

Lefevre  crossed  Silver  Spangled  Hamburgs  and  Brown  Leghorns. 
The  spangling  was  found  to  be  a  sex-linked  dominant  factor.  A  span- 
gled cock  bred  to  a  Leghorn  hen  gives  spangled  sons  and  daughters;  a 
spangled  hen  by  a  Leghorn  male  gave  spangled  sons  and  not  spangled 
daughters.  The  daughters  do  not  transmit  spangling.  Other  factors 
may  obscure  the  results,  especially  factors  for  black,  or  the  localization 
of  the  pattern.  Lefevre  says  "it  would  seem  probable  that  multiple 
factors  for  black,  introduced  by  the  Brown  Leghorns,  are  present,  and 
that  these  factors  may  have  a  cumulative  effect,  with  the  result  that 
pigmentation  is  developed  to  varying  degrees  of  extension."  Whether 
the  factors  for  black  spoken  of  as  coming  from  the  Leghorns  are 
dominant  wild-type  factors  that  have  mutant  allelomorphs  in  the  Silver 
Spangled  Hamburg  is  not  entirely  clear  from  the  quotation. 

Baur  gives  in  his  Introduction  to  the  Study  of  Heredity  (1914, 
pp.  202-203)  some  results  (unpublished)  that  Hagedoorn  had  obtained 
by  crossing  gold  and  silver  races  of  Assendelver  birds.  The  factor 
is  sex-linked  and  is  no  doubt  the  same  factor  reported  by  Jones  for 
gold  and  silver  Campines  and  by  Sturtevant  for  Columbian  Wyan- 
dottes.  Silver  dominates  gold  and  the  sex  relations  are  the  same  as 
those  already  reported  by  others  for  poultry,  viz,  the  male  is  ZZ,  the 
female  ZW.  Gold  hens  by  a  heterozygous  silver1  gave  162  silver  cocks, 
163  silver  hens,  168  gold  cocks,  160  gold  hens,  expressed  graphically 
(g  for  gold,  s  for  silver) : 

Zg-W9XZ  — Z^cT 
Z*Z»—  Z"Z"— Z3W— z»w 

Silver      Gold     Silver    Gold 
male       male    female  female 

When  a  silver  hen  was  united  to  a  gold  cock  there  were  246  silver 
cocks  and  243  gold  hens — crisscross  inheritance. 

Summary. 

From  the  standpoint  of  the  Brown  Leghorn  type  representing  the 
wild  type,  the  following  colors  and  patterns  represent  dominant 
mutations  from  that  type: 

Dominants. 
White  of  White  Leghorn.  Barring  of  Plymouth  Rock. 

Silver  of  Dark  Brahma.  Black  (?)  of  Plymouth  Rock. 

Black  of  Minorca.  Buff  (or  red). 

Lacing  of  Brahma. 

1  No  mention  is  made  by  Baur  that  a  heterozygous  male  instead  of  a  pure  silver  male  was  used, 
although  the  male  is  made  heterozygous  in  the  formulae. 


RELATING   TO    SECONDARY    SEXUAL    CHARACTERS.  31 

Each  of  these  (in  heterozygous  condition  of  course)  is  dominant; 
in  some  cases  completely  so,  in  others  incompletely  dominant.  At 
three  different  loci  in  the  sex  chromosome  a  dominant  mutation  has 
occurred ;  at  three  loci  in  other  chromosomes  dominant  mutant  changes 
have  also  occurred. 

Recessives. 

White  of  Rose  Comb  bantam.  Brown  of  Brown-breasted  game. 

White  of  Silky.  Penciling. 

White  of  White  Rock. 

Whether  the  recessive  white  that  is  sometimes  found  in  dominant 
White  Rock  stock  is  different  from  both  of  the  other  recessive  whites 
is  not  known.  There  are,  then,  5  or  6  recessive  characters  that  are  not 
sex-linked  and  1  recessive  sex-linked  character. 

Owing  to  the  relatively  large  number  of  color  dominants  in  poultry, 
some  unnecessary  confusion  has  arisen  concerning  the  relation  of  the 
dominants  to  the  wild  type,  and  especially  to  other  mutant  characters 
to  which  they  are  said  to  be  dominant,  in  the  sense,  however,  of  being 
epistatic.  An  imaginary  example  will  illustrate  this.  For  example, 
if  at  some  locus  in  the  wild  type  a  mutation  occurred  that  gave  a 
dominant  black  (i.  e.,  a  black  that  shows  up  when  one  gene  for  it  is 
present)  and  at  the  same  time  this  black  also  showed  up  even  when 
other  recessive  mutant  characters  were  present  in  homozygous  form, 
then  Fi  birds  would  be  black  when  black  is  crossed  to  such  pure 
recessive  stocks.  Such  cases  have  indeed  been  described  as  dominant, 
but  a  knowledge  of  F2  would  have  shown  at  once  the  error  of  such  a 
system.  For,  if  black  had  been  a  real  dominant,  the  F2  would  have 
given  3  blacks  to  1  of  the  other  type  (such  as  the  wild  type),  but  if  the 
case  were  one  of  epistasis,  then  there  would  have  been  9:3:3:1 
classes  in  F2  (or  some  modification  of  that  ratio).  In  this  sense,  then, 
epistasis  may  be  defined  as  a  result  that  appears  when  one  member  of 
the  pair  of  genes  produces  its  effect  regardless  of  the  constitution  of  the 
individual  with  respect  to  another  gene  (or  other  pairs  of  genes).  It 
is  curious  at  least  to  note  that  in  the  case  of  dominant  white  the  term 
epistatic  has  been  much  less  often  used  than  in  the  case  of  black. 
Theoretically  the  two  situations  are  exactly  alike,  but  because  black 
could  so  obviously  conceal  things  beneath  it,  while  white  is  not  thought 
of  as  doing  so,  it  seemed  "natural"  to  make  such  a  distinction.  In 
reality  it  is  not  a  question  of  covering  up  at  all,  but  a  case  of  a  dominant 
character  (white  or  black)  preventing  other  colors  from  appearing. 

In  the  case  of  recessive  white  the  situation  is  somewhat  different 
and  no  one,  so  far  as  I  know,  has  gone  so  far  as  to  speak  of  such  a  white 
as  epistatic,  although  when  the  animal  is  white  it  certainly  hides,  when 
completely  effective,  all  the  other  effects  of  color-producing  factors, 
but  allows  them,  to  "show  through"  in  some  of  the  cases.  This 
means  not  that  they  do  "show  through,"  but  that  they  only  develop 


32  THE    GENETIC    AND    THE    OPERATIVE    EVIDENCE 

to  a  "lower"  degree.  The  difference  between  dominant  and  recessive 
whites  rests  on  the  fact  that  in  one  case  one  member  of  a  pair  of  fac- 
tors gives  white  and  in  the  other  both  members  are  necessary.  But 
obviously  such  a  distinction  is  not  important,  and  if  it  were  worth 
while  the  case  might  be  argued  for  recessive  whites  being  also  epistatic. 
The  whole  tangle  goes  back  to  a  false  interpretation  of  presence  and 
absence  of  characters  and  presence  and  absence  of  factors.  As  I  have 
gone  over  this  ground  recently  in  my  paper  on  the  Theory  of  the  Gene, 
I  need  not  repeat  here  what  I  tried  to  make  clear  there. 

ENDOCRINE  CELLS  IN  OVARY  AND  TESTES  OF  BIRDS. 

The  occurence  of  gland-like  cells  with  an  internal  secretion  in  the 
ovary  and  testes  of  fowls  has  been  described  by  a  number  of  writers 
and  denied,  at  least  for  the  testes,  by  others.  The  work  of  Boring  and 
Pearl  has  done  much  to  bring  this  question  to  a  satisfactory  solution, 
for  they  have  tested  out  and  made  use  of  the  best  reagents  that  their 
predecessors  had  discovered  and  have  used  a  much  greater  amount  of 
material.  As  they  have  reviewed  very  fully  the  literature  of  the  subject, 
it  will  not  be  necessary  to  go  over  the  ground  again  in  detail. 

In  the  follicles  of  the  ovary  there  are  present,  according  to  Boring 
and  Pearl,  groups  or  nests  of  cells  lying  among  the  connective  tissue  of 
the  inner  theca.  The  cells  are  about  three  times  as  large  as  the  ordi- 
nary connective-tissue  cells  of  the  ovary.  The  cytoplasm  is  clear  and 
vacuolated,  "only  occasionally  containing  a  few  acidophile  granules 
which  stain  with  the  fuchsin  in  Mallory's  stain  or  the  eosin  of  Mann's 
stain,  while  the  real  interstitial  cells  are  crowded  with  granules." 

When  the  egg  is  set  free  from  its  follicle,  the  latter  collapses  and  the 
rupture  becomes  closed.  A  mass  of  cells  collects  in  the  center  of  the 
collapsed  structure  which  develop  yellow  pigment.  The  cells,  lying  in 
the  puckered  edge  of  the  follicle,  may  also  develop  such  yellow  color. 
The  cells  that  produce  the  yellow  pigment  come  from  the  nests  of  cells 
that  lay  originally  mainly  in  the  theca  interna.  Either  by  migration 
or  by  division  they  come  to  fill  up  the  central  cavity.  The  yellow 
substance  in  the  cells  is  not  fat,  since  it  does  not  dissolve  in  the  clearing 
oils,  nor  can  it  be  protein,  for  it  does  not  take  acid  stains  as  normal 
secretion  granules  of  protein.  It  does  not  dissolve  in  HC1,  HN03, 
or  H2S04,  nor  in  strong  KOH,  although  the  latter  turns  the  pigment  a 
bright  red  color.  Many  other  substances  were  also  tried  by  Boring  and 
Pearl,  but  none  of  them  dissolved  the  yellow  pigment,  which  reacts 
in  this  respect  in  the  same  way  as  does  the  yellow  pigment  in  the 
luteal  cells  of  the  mammal.  The  similarity  in  the  nature  of  the  pig- 
ments in  the  two  cases  is  an  argument  in  favor  of  the  view  that  the 
cells  that  produce  the  pigment  are  the  same  in  both  groups.    In  the 


RELATING    TO    SECONDARY    SEXUAL    CHARACTERS.  33 

mammal  the  yellow  corpus  luteum  is  a  large,  gland-like  organ  that 
develops  after  the  ovum  is  discharged;  in  the  bird  there  is  also  a  yellow 
spot  on  the  ovary,  due  to  the  pigment  in  the  collapsed  follicle,  but  it  is 
smaller  and  much  less  conspicuous  than  in  the  mammal.  The  evidence 
concerning  luteal  cells  in  the  testes  of  the  bird  is  conflicting.  One  of 
the  difficulties  in  the  situation  is  the  identification  of  the  cells,  which 
are  sometimes  regarded  merely  as  the  general  connective-tissue 
stroma  of  the  testis  that  is  undoubtedly  present;  at  other  times  special 
secretory  cells  are  discerned  embedded  in  the  connective  tissue,  as 
individual  cells  or  in  islands.  Boring  states  (1912)  that  in  newly 
hatched  chicks  about  half  of  the  tissue  of  the  testes  is  interstitial  con- 
nective tissue;  the  other  half  consists  of  tubes  or  cords  whose  principal 
function  is  the  development  of  the  germ-cells.  In  the  paper  of  1912 
Boring  reached  the  conclusion  that  there  are  no  "interstitial  cells  in 
the  testes  of  the  domesticated  chicken  in  the  sense  that  this  term  has 
been  previously  used,"  and  states  that  no  evidence  has  been  found  that 
an  internal  secretion  of  any  kind  is  formed  by  any  cells  of  the  interstitial 
tissue. 

It  is  not  necessary  to  discuss  whether  or  not  connective-tissue  cells 
are  present  in  the  testes  of  birds,  for  is  it  generally  conceded  that  they 
are  found  at  least  in  certain  stages,  but  it  is  important  to  look  into  the 
question  as  to  whether  among  these  interstitial  cells  there  are  others 
that  have  an  endocrine  function.  Mazzetti  gives  pictures  of  such 
gland-cells  between  the  seminal  tubules  of  the  cock  bird,  but  says  that 
they  are  rare,  "even  though  this  bird  has  very  marked  secondary 
sexual  characters"  (Boring  and  Pearl).  It  maybe  remarked  parenthet- 
ically that  if  they  had  been  more  abundant  the  bird  might  have  had 
no  secondary  sexual  plumage  since  it  will  be  pointed  out  below  that  such 
glandular  cells  may  have  as  their  special  function  the  suppression  of 
these  characters. 

According  to  Des  Cilleuls,  interstitial  cells  are  first  found  in  males 
about  30  days  old  and  at  this  time  the  secondary  sexual  characters  put 
in  their  appearance.  If,  as  will  be  shown  in  the  sequel,  he  means  by 
interstitial  cells  the  endocrine  cells  that  suppress  the  development  of 
the  male  plumage  in  the  female,  the  appearance  of  these  cells  at  this 
time  would  be  significant;  but  if  he  implies  that  their  occurrence  in 
the  male  incites  the  development  of  the  secondary  sexual  characters, 
his  interpretation  is  open  to  serious  doubt.  Reeves  found  interstitial 
cells  in  testes  of  cocks  3,  5|,  9,  and  18  months — more  in  the  earlier 
stages. 

In  a  later  communication  by  Boring  and  Pearl  the  whole  question 
is  taken  up  again  with  improved  methods,  etc.  Previously  21  male 
birds  had  been  studied,  just  hatched  to  12  months  old.  More  Mo- 
tions of  this  same  material  were  made  which  were  stained  according 


34       THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

to  Mann's  and  Mallory's  methods.  In  addition,  a  whole  new  series 
of  preparations  was  made.  A  few  interstitial  cells,  i.  e.,  granule  con- 
taining-cells  were  found  in  newly  hatched  chicks,  but  not  in  any  of 
the  60  mature  birds  examined. 

LUTEAL-CELLS  IN  THE  TESTES  OF  THE  MALE  SEBRIGHT. 

Finding  that  the  testes  of  F2  hen-feathered  birds  were  often  flat  and 
pear-shaped  instead  of  rounded  and  cylindrical,  as  in  ordinary  cocks, 
and  that  they  were  often  black  in  color,  suggested,  as  already  stated, 
that  the  testes  of  the  Sebright  might  be  hermaphrodite  in  some  element. 
It  seemed  not  impossible  that  egg-cells  might  be  found.  I  made  a 
considerable  number  of  sections  of  the  testes  of  these  birds  and 
examined  them  under  the  microscope;  not  finding  any  egg  or  egg-like 
bodies,  the  slides  were  laid  aside,  but  the  idea  that  in  some  other  way 
the  Sebright's  testes  might  correspond  to  the  ovary  of  the  female  next 
recurred  to  my  mind.  Consequently,  when  in  the  summer  of  1918  I 
had  some  new  material  derived  from  a  castrated  Sebright  male  that 
had  partly  regenerated  its  testes  and  was  again  going  back  to  hen- 
feathering,  and  pieces  from  one  of  the  old  testes  of  a  castrated  bird, 
I  asked  Miss  Boring,  who  was  then  in  Woods  Hole,  to  make  some 
preparations  and  examine  them  to  see  if  she  could  detect  any  such 
elements  in  them  as  she  had  found  in  the  female.  Miss  Boring 
reported  the  occurrence  of  luteal  cells  in  the  testes  from  hen-feathered 
males,  and  the  results  have  been  published  in  a  brief  preliminary  paper 
(1918).  The  abundance  of  these  clear  cells,  supposedly  gland-cells 
with  endocrine  influences,  in  the  testes  of  hen-feathered  birds  is  in 
sharp  contrast  to  their  absence  in  the  normal  adult  cock  birds.  It 
seems  to  follow,  therefore,  that  the  hen-feathering  in  the  Sebrights  is 
due  to  the  presence  of  these  cells,  whose  function  is  the  same  as  of  the 
similar  cells  in  the  female,  i.  e.,  the  suppression  in  both  of  cock-feather- 
ing. Castrating  the  Sebright  produces  its  effect  by  the  removal  of 
these  cells  that  are  responsible  for  the  suppression  of  cock-feathering. 

The  occurrence  of  luteal  cells  in  young  stages  of  other  races  of  poultry 
raises  the  question  as  to  whether  in  these  races  the  first  or  juvenile 
plumage,  that  resembles  that  of  the  hen  rather  than  that  of  the  cock, 
may  not  also  be  due  to  an  internal  secretion  from  these  cells,  or  whether 
this  juvenile  plumage  is  only  the  plumage  of  a  characteristic  stage  in 
development.  Castration  of  young  chicks  ought  to  settle  this  point. 
Such  castration  experiments  have  been  made  by  Goodale.  The 
absence  of  any  reference  to  any  effect  on  the  juvenile  plumage  in 
these  early  castrated  birds  probably  meant  that  they  did  not  develop 
precociously  cock-feathering,  and  he  writes  me  that  he  examined  them 
carefully  and  that  their  plumage  is  like  that  of  the  normal  chicks. 
Geoffrey  Smith  has  reported  the  occurrence  of  two  kinds  of  males 


RELATING    TO    SECONDARY    SEXUAL    CHARACTERS.  35 

in  a  race  of  Leghorns,  the  males  of  one  of  which  become  cock-feath- 
ered before  the  other.  May  not  this  difference  depend  on  the  length 
of  time  endocrine  cells  remain  or  begin  to  develop?  A  histological  study 
of  the  two  types  would  be  of  the  greatest  interest. 

ENDOCRINE  CELLS  IN  THE  TESTES  OF  MAMMALS. 

In  man  and  other  mammals  it  has  long  been  recognized  that  in 
addition  to  the  germinal  cells  of  the  testis  there  are  also  present  other 
cells,  sometimes  called  interstitial  cells,  that,  so  far  as  known,  have  no 
immediate  function  in  connection  with  the  germ-cells,  or  at  least  that 
have  other  important  functions  outside  the  relation  to  the  reproductive 
organ.  That  some  internal  secretion  from  these  cells  has  an  important 
influence  on  the  secondary  sexual  characters  rather  than  anything  done 
by  or  produced  by  the  germinal  cells  has  been  very  clearly  shown  by 
evidence  derived  from  three  separate  sources,  namely,  from  the 
operation  known  as  vasectomy,  from  an  exceptional  condition  known 
as  cryptorchidism,  and  more  indirectly  from  X-ray  treatment.  Vasec- 
tomy involves  either  cutting  the  vasa  deferentia  in  such  a  way  that 
the  cut  ends  do  not  reunite.  In  consequence  of  the  closure  of  the 
outlet  of  the  testis  the  germinal  cells  slowly  degenerate,  and  finally 
completely  disappear.  How  such  an  effect  is  produced  we  do  not  know. 
That  this  result  does  take  place  is  borne  out  by  the  unanimous  testi- 
mony of  all  those  who  have  successfully  performed  the  operation. 
Ancel  and  Bouin  showed  (1903)  that  breaking  the  continuity  of  the 
vas  deferens  suppressed  spermatogenesis  in  8  to  12  months.  Both 
the  Sertoli  cells  (the  nourishing  cells  of  the  germinal  epithelium)  and 
the  interstitial  cells  persist.  Such  animals  remain  sexually  active  and 
their  secondary  sexual  characters  are  not  affected.  Marshall  states 
that  in  the  hedgehog  the  remarkable  periodic  enlargement  of  the 
testis  takes  place  even  after  vasectomy,  although  the  germ-cells  have 
disappeared. 

In  mammals  the  testes  fail  at  times  to  pass  through  the  inguinal 
canal,  and,  in  consequence  of  their  retention  in  the  body-cavity,  the 
germ-cells  fail  to  develop.  On  the  other  hand,  the  interstitial  cells 
of  the  testis  develop  normally.  Cryptorchid  individuals  show  the 
normal  secondary  sexual  characters  of  their  species.  How  retention 
of  the  sperm  should  give  rise  to  the  same  result  as  cutting  the  duet, 
viz,  absorption  of  the  germinal  cells,  is  not  known.  A  possible  solution 
may  be  found  in  the  pressure  exerted  on  the  testes,  both  when  retained 
in  the  abdomen  and  when  their  outlets  are  stopped  by  tying  or  cut  tint: 
the  ducts. 

Finally,  it  has  been  long  known  that  continued  or  repeated  exposure 
to  X-rays  or  to  radium  causes  the  destruction  of  the  germ-cells,  but 
leaves  the  interstitial  cells  intact  and  presumably  functional.    Destruc- 


36       THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

tion  of  the  germ-cell  by  X-rays  has  no  effect  on  the  secondary  sexual 
characters. 

This  threefold  evidence  demonstrates  that  in  the  male  of  the  mam- 
malia most,  perhaps  all,  of  the  secondary  sexual  characters  that  are 
affected  by  castration  are  not  affected  by  the  destruction  of  the  germ- 
cells.  This  conclusion  supports  very  strongly  the  view  that  the  inter- 
stitial cells  are  the  cellular  element  in  the  testes  that  influence  through 
internal  secretion  the  development  of  the  secondary  sexual  characters 
of  the  male. 

Equally  important  are  the  results  that  relate  to  the  accessory  organs 
of  reproduction,  such  as  the  glands  that  open  into  the  vas  deferens 
(prostate,  Cowper's  gland,  etc.)  and  the  copulatory  organs  also.  In 
the  castrated  mammals  these  organs  diminish  in  size.  On  the  other 
hand,  after  destruction  of  the  germ-cells  in  the  testes  (or  even  when 
they  fail  to  develop  as  in  cryptorchid  individuals)  these  accessory  parts 
are  unaffected.  In  birds,  as  will  be  shown,  the  situation  is  entirely 
different. 

CYCLICAL  CHANGES  IN  THE  INTERSTITIAL  CELLS  IN 
HIBERNATING  MAMMALS. 

The  changes  that  take  place  in  the  interstitial  cells  in  mammals  that 
hibernate  and  in  which  there  is  a  definite  rutting  season  following 
hibernation  have  been  examined  by  several  workers.  The  mole  has 
been  studied  by  Regaud  (1904),  Lecaillon  (1909),  Tandler  and  Grosz 
(1911);  the  marmot  by  Hauseman  (1895)  and  Gaugini  (1903);  the 
hedgehog  by  Marshall  (1911);  and  the  woodchuck  by  Rasmussan 
(1917).  In  the  mole  the  interstitial  cells  are  most  abundant  when  the 
tubules  in  which  the  spermatogenesis  is  taking  place  are  least  devel- 
oped, and  vice  versa.  In  the  hedgehog  the  increase  in  both  tissues  takes 
place  at  the  same  time.  In  the  woodchuck  both  tissues  increase  rapidly 
after  hibernation  (during  March  and  April),  after  which  the  spermato- 
genesis continues  actively  for  the  two  following  months  (May  and 
June),  while  the  interstitial  cells  retrograde  rapidly  during  April  and 
remain  at  a  low  level  for  the  rest  of  the  year.  Retrogression  in  the 
germinal  epithelium  begins  in  July,  after  the  rutting  season  is  past. 
It  appears  from  this  evidence  that  the  activity  of  the  two  tissues  does 
not  always  run  the  same  course.  Since  the  secondary  sexual  characters 
of  the  male,  which  are  not  well  developed  in  these  animals,  are  not  so 
far  as  known  affected  by  the  condition  of  the  testes,  the  evidence  does 
not  have  any  very  direct  bearing  on  our  present  topic.  How  far  the 
sexual  behavior  of  these  mammals  is  determined  by  the  quantity  or  by 
the  activity  of  the  interstitial  cells  is  not  very  clear  from  the  evidence, 
although  there  is  a  very  noticeable  increase  in  the  amount  of  this 
tissue  just  before  and  during  the  rutting  season.    In  the  mole  also  the 


RELATING    TO    SECONDARY    SEXUAL    CHARACTERS.  37 

interstitial  cells  begin  to  increase  just  before  the  mating  season,  and 
the  increase  continues  for  several  months  after  mating  has  taken  place. 
It  is  difficult  to  judge  how  great  or  how  little  the  change  amounts  to 
unless  the  whole  organ  is  considered,  for  the  relative  volumes  of  the 
seminal  tubes  and  the  interstitial  tissues  does  not  give  a  measure  of  the 
total  volume  of  these  tissues,  since  the  testes  may  decrease  greatly 
in  size  when  the  seminal  tubes  retrograde,  and  the  apparent  increase 
of  the  interstitial  cells  at  the  time  may  not  increase  the  total  amount 
of  that  tissue  present. 

Probably  more  important  than  the  ratio  of  interstitial  tissue  to 
tubules  is  the  activity  of  the  former.  Rasmussan  states  that  in  the 
woodchuck  the  interstitial  cells  not  only  increase  in  number  immedi- 
ately after  hibernation,  but  the  increase  in  amount  of  this  tissue  is 
largely  due  to  increase  in  the  cytoplasm,  in  which  there  appears  an 
accumulation  of  fatty  globules  in  the  more  peripheral  parts  of  the  cells. 
In  the  central  cytoplasm  an  abundance  of  fine  lipoid  granules  develops. 

Marshall  has  made  some  interesting  experiments  on  the  hedgehog 
at  different  seasons.  Castration  in  March  prior  to  the  breeding- 
season  has  an  influence  on  the  accessory  generative  organs  (vesicuke 
seminales,  prostates,  and  Cowper's  glands).  They  remain  in  the  same 
undeveloped  stage  in  which  they  were  at  the  time  of  operation.  If 
castration  is  carried  out  very  early  in  the  breeding-season,  when  the 
accessory  reproductive  organs  are  about  half  developed,  their  further 
enlargement  is  prevented.  In  so  far  as  the  accessory  organs  rank  as 
secondary  sexual  organs,  their  complete  development  is  thus  shown 
to  depend  on  the  testes.  Transection  of  the  vasa  deferentia  before  the 
beginning  of  the  breeding-season  affects  somewhat  the  enlargement  of 
the  testes,  but  produces  no  effect  on  the  accessory  organs. 

HERMAPHRODITISM  IN  POULTRY  AND  THE  SECONDARY  SEXUAL 

CHARACTERS. 

Several  hermaphrodite  birds  have  been  described  (Brandt,  1889; 
Shattock  and  Seligman,  1906;  Pearl  and  Curtis,  1909;  Smith  and 
Thomas,  1913;  Bond,  1914;  etc.).  The  most  recent  and  complete 
account  of  such  birds  is  that  by  Boring  and  Pearl.  They  examined  in 
all  8  hermaphrodites,  or  at  least  8  birds  that  showed  in  their  plumage, 
or  other  secondary  sexual  characters,  peculiarities  of  both  Bexes.  Five 
of  the  birds  came  from  Herr  Houwink  in  Meppel,  Holland,  who  had  a 
stock  in  which  there  appeared,  in  1911,  two  hermaphrodites  out  of  80 
birds,  and  in  1912,  three  out  of  80  birds.  These  were  the  birds  studied 
by  Boring  and  Pearl.  In  addition,  when  Pearl  saw  Horr  Houwink'a 
birds  in  1910,  "  there  were  then  on  hand  a  considerable  Dumber  of  these 
supposed  hermaphrodite  birds."  An  anatomical  study  of  the  Holland 
birds  showed  that  one  of  them  was  nearly  a  normal  female;  three,  the 


38       THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

authors  say,  were  ''evidently  undeveloped  females.  They  have  infantile 
oviducts  and  embryonic  ovaries."  It  should  be  added  that  there  was  a 
tumor  more  than  twice  the  size  of  the  ovary  attached  to  or  part  of  the 
ovary.  If  the  ovary  itself  was  affected  by  the  tumor,  or  the  tumor  was 
a  part  of  the  ovary,  the  slightly  unusual  condition  of  the  birds  might 
be  accounted  for.  Of  the  other  3  birds,  2  are  also  suspected  to  have 
ovarian  tumors,  while  in  the  third  bird  streaks  of  a  secretion  which 
resembles  the  substance  of  the  tumor  of  the  other  two  were  found. 
The  change  towards  male  plumage  in  these  5  birds  is  probably  due 
either  to  the  incomplete  development  of  ovary  or  to  the  effect  of  the 
tumor  on  the  ovary.  Although  luteal  cells  are  described  as  present,  it 
seems  probable  that  their  total  number  might  be  less  than  in  a  normal 
bird,  and  hence  their  insufficient  secretion  would  fail  to  suppress  the 
development  of  male  plumage.  From  this  point  of  view  these  birds 
are  no  more  hermaphrodites  than  is  a  hen  with  her  ovary  taken  out. 

The  remaining  Holland  birds  were  entirely  different.  On  the  left 
side  there  was  an  ovary  in  an  inactive  condition ;  on  the  right  side  there 
was  a  testis,  producing  spermatozoa.  Sections  of  the  testis  show 
that  it  is  normal,  consisting  of  a  mass  of  tubules  with  very  little  con- 
nective tissue  between  them.  In  both  ovary  and  testis  there  are  "a 
few  nests  of  luteal  cells  near  the  surface.  The  ovary  contains  eggs,  but 
is  abnormal  to  some  extent."    The  authors  state: 

"In  external  appearance  it  is  more  like  a  male  than  the  others,  which  fact 
correlates  well  with  the  active  condition  of  the  testis  and  inactive  diseased 
ovary,  with  only  one  corpus  luteum  scar.  The  interstitial  cells  can  scarcely 
be  held  accountable  for  the  male  secondary  sex  characters,  as  the  only  ones 
in  an  active  secreting  condition  are  a  few  in  the  ovary." 

It  is  not  quite  clear  what  is  meant  in  this  quotation  by  the  statement 
that  the  interstitial  cells  can  scarcely  be  held  accountable  for  the  male 
secondary  characters  unless  to  suggest  that  they  cause  the  development 
of  these  characters  in  the  male,  as  they  are  supposed  to  do  in  mammals — 
a  view  that  the  authors  do  not  seem  at  other  times  to  hold. 

Another  hermaphrodite  (Atwood's  black)  had  an  infantile  oviduct 
and  an  ovotestis.  A  second  bird,  too,  had  an  ovotestis — mostly 
testis — as  well  as  a  rather  large  oviduct.  Collections  of  luteal  cells 
are  described  between  the  tubules  of  the  testicular  portion.  If,  as 
suggested  by  the  Sebright  cases,  these  cells  tend  to  suppress  the  female 
plumage,  their  presence  here  in  excess  might  at  least  be  made  to  account 
for  the  female  part  of  the  plumage  of  this  bird.  Comparing  the  last 
two  birds  (that  showed  active  sex-behavior  as  males)  with  the  best 
of  the  Holland  birds,  Boring  and  Pearl  point  out  that  the  active  sex 
behavior  of  the  two  former  can  not  be  due  to  "interstitial  cells  that  are 
absent  in  these  but  present  to  a  slight  extent  in  the  former."  They 
then  add  " ....  though  the  differences  can  not  be  laid  to  the  lutear  cells, 


RELATING   TO   SECONDARY    SEXUAL   CHARACTERS.  39 

as  they  are  present  in  all  three."  That  the  relative  amounts  of  the 
latter  or  their  activity  might  still  be  accountable  for  the  difference 
would  not  seem  entirely  excluded  from  the  evidence  so  far  as  it  is  given. 

A  fourth  hermaphrodite  (Dexter's)  laid  12  eggs  and  had  a  large 
coiled  oviduct.  There  was  present  "a  large,  lobulated  reproductive 
organ  on  the  left,"  which  proved  to  be  an  ovotestis.  Several  ovarian 
tumors  were  present  and  there  was  testicular  tissue. 

It  is  fairly  evident,  then,  that  four  of  these  birds  described  by  Boring 
and  Pearl  were  females  with  abnormal  ovaries.  The  incomplete 
development  of  the  latter,  or  their  abnormal  condition  due  to  tumors, 
may  sufficiently  explain  the  occurrence  of  male  secondary  sexual 
characters.  That  these  tumors  affect,  to  different  degrees,  such  charac- 
ters is  expected  from  what  is  shown  by  imperfectly  spayed  females  of 
normal  breeds. 

There  are  a  few  statements  in  the  summary  of  this  paper  that  call  for 
comment.  The  statement  that  the  "development  of  comb,  spurs, 
and  wattles  does  not  stand  in  direct  quantitative  relation  to  the  Bex 
of  the  gonad,"  appears  to  be  only  intended  as  a  statement  of  fact  based 
on  the  author's  observation.  But  in  what  sense  is  there  an  expectation 
that  they  should  stand  in  such  relation  beyond  the  obvious  fact  that 
in  the  cock  the  comb  and  wattles  are  larger  than  in  the  hen,  and  that 
spurs  are  generally  present  only  on  the  cock.  But  if  the  expression 
"sex  of  the  gonad"  implies  the  germ-cells  it  is  not  at  all  certain  that 
there  is  any  expectation  of  a  quantitative  relation,  and  there  is  some 
probability  at  least  that  other  cells  than  the  sex-cells  are  involved  in 
the  development  of  combs,  wattles,  and  possibly  spurs.  A  castrated 
cock  has  a  small  comb  resembling  that  of  the  female  bird.  On  the 
other  hand,  removal  of  the  ovary  sometimes  leads  to  an  increase  in  the 
comb  and  wattles.  Here  we  have,  to  say  the  least,  a  paradoxical 
situation,  for  the  result  looks  superficially  as  though  something  in  the 
ovary  keeps  down  the  hen's  comb,  while  something  in  the  testes  kei 
up  the  cock's  comb,  yet  when  the  ovary  is  removed  the  hen  develops 
a  cock's  comb;  when  the  testes  are  removed  the  cock  develops  a  hen  'a 
comb.  The  real  meaning  is,  I  think,  that  the  genetic  complex  for 
femaleness  (one  Z  or  else  ZW)  stands  in  itself  for  a  full-sized  comb, 
while  the  genetic  complex  for  maleness  (two  Z's)  stands  in  itself  for 
small  comb. 

Boring  and  Pearl  state  that  "body-shape  and  carriage  have  a  genetic 
relation  to  the  sex  of  the  gonad."  This  statement  means,  I  think, 
that  the  amount  of  testicular  matter  present  stands  in  some  direct 
relation  to  the  shape  of  the  body  and  carriage  of  the  male.  ( lastratioo, 
both  of  the  normal  cock  and  the  Sebright,  seems  to  change  the  carri- 
age somewhat  and  perhaps  the  shape.  Both  lose  something  of  the 
peculiar  attitude  of  the  male,  but  I  have  not  been  able  to  my  own 


40       THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

satisfaction  to  analyze  what  this  means.  As  has  been  pointed  out,  and 
as  the  pictures  show,  the  castrated  Sebright  changes  his  attitude,  but 
whether  this  is  a  change  due  to  his  new  contour,  or  to  a  new  balance 
resulting  from  a  large  tail,  or  to  a  let-down  resulting  principally  from 
effects  on  the  nervous  system,  is  difficult  to  determine.  The  same 
statements  apply  in  part  to  the  castrated  cock  of  ordinary  breeds,  but 
not  to  the  same  degree,  since  the  change  after  castration,  in  feathering 
and  in  carriage  at  least,  is  slight. 

The  conclusions  that  the  "amount  of  lutear  cells  or  pigment  (?)  is 
in  precise  correlation  with  the  degree  of  external  somatic  femaleness 
exhibited  by  the  individual"  is  of  especial  interest  in  connection  with 
the  Sebright  evidence.  It  is  difficult,  however,  to  gather  from  the 
body  of  the  paper  what  the  absolute  amount  of  luteal  cells  is  that  is 
present,  for  even  in  some  of  the  more  male-like  birds  with  an  ovotestis 
the  description  leads  one  to  suppose  that  there  may  be  as  much  luteal 
material  present  as  in  some  of  the  more  female  birds  with  infantile 
ovaries  or  cystic  tumors. 

Pearl  and  Curtis  (1909)  described  "a  case  of  incomplete  herma- 
phroditism" in  a  Barred  Plymouth  Rock  fowl.  Externally  the  bird 
looked  like  a  hen,  but  "the  head  and  neck  resembled  these  parts  in 
the  cockerel,"  especially  the  comb  and  wattles.  The  bird  was  never 
seen  to  tread  a  hen,  nor  did  it  ever  crow  normally.  An  ovary  and 
oviduct  were  found  on  the  left  side,  the  former  no  larger  than  that  of  a 
laying  hen  after  removal  of  the  large  yolks.  No  eggs  were  visible  on 
its  surface.  On  the  right  side  a  testis  (9  mm.  by  6  mm.)  and  vas 
deferens  were  present.  No  eggs  were  found  in  the  ovary,  and  it  gave 
every  indication  of  being  in  a  degenerating  condition,  with  no  eggs 
or  egg  follicles  in  it.  The  testis  had  no  "normal  seminiferous  tubules," 
but  indications  of  cellular  rods  were  present.  The  organ  is  in  all 
probability  a  degenerating  testis. 

A  Leghorn  2  years  old  has  been  described  by  Shattuck  and  Selig- 
mann  (1906)  that  had  the  full-developed  comb  and  wattles  of  the 
cock,  but  the  former  drooped  slightly  to  one  side  as  in  the  hen.  Well- 
developed  spurs  were  present.  The  plumage  was  mainly  female,  with 
neck-hackles  moderately  developed,  and  with  "saddle-hackles"  prac- 
tically absent.  The  tail,  though  not  typically  female,  lacks  sickle 
feathers.  The  bird  excited  no  notice  from  other  birds  of  either  sex. 
A  large  left  oviduct  and  the  distal  end  of  a  right  oviduct  were  present. 
Two  vasa  deferentia  were  also  present.  In  the  left  side  a  flattened  sex- 
gland  (3  cm.  high)  was  found,  made  up  of  testicular  tubules.  Two 
small  ova  were  found  in  its  posterior  end.  The  right  gonad  was  also 
tubular  (testis). 

The  occurrence  of  real  testicular  tissue  in  one  of  the  Holland  birds 
and  in  three  others  described  by  Boring  and  Pearl,  as  well  as  in  one 


RELATING    TO    SECONDARY    SEXUAL    CHARACTERS.  41 

described  by  Pearl  and  Curtis,  and  in  another  by  Shattuck  and  Selig- 
mann  calls  for  special  comment,  since  the  presence  of  both  testicular 
and  ovarian  tissue  in  the  same  bird  is  the  essence  of  hermaphroditic  a. 
In  general  there  are  two  ways  of  looking  at  such  a  result.  Either  the 
sex-determining  factors  have  been  changed  so  that  in  one  part  of  the 
body,  where  the  reproductive  organs  are  laid  down,  one  condition  can 
prevail,  in  other  parts  other  conditions;  or  a  mixup  of  the  sex  chromo- 
somes has  taken  place.  Until  we  get  some  more  evidence  concerning 
such  cases  it  is  useless  to  speculate,  although  the  former  view  might 
seem  the  most  probable  of  the  two  if  the  Holland  birds  of  Herr  Hou- 
wink's  flock  were  in  a  high  degree  true  hermaphrodites. 

But  in  fact  three  of  the  four  described  by  Boring  and  Pearl  were 
due  to  tumors  of  the  ovary,  which,  if  they  suppress  the  normal  develop- 
ment of  this  organ,  would  be  expected  to  call  forth  the  appearance  of 
the  secondary  sexual  characters  of  the  cock.  If  the  likelihood  of 
developing  a  tumor  were  inherited,  the  frequent  occurrence  of  hen- 
feathered  birds  in  this  flock  would  be  explained.  However,  one  true 
hermaphrodite  in  4  birds  is  surprisingly  high  for  a  chance  result,  since 
hermaphrodite  birds  are  very  rare. 

The  second  interpretation  suggested  above  is  one  that  has  been 
advanced  and  established  by  genetic  evidence  in  Drosophila,  viz, 
dislocation  of  the  sex  chromosomes.  In  the  case  of  birds  the  male  is 
supposed  to  be  duplex  for  the  sex  factors  (ZZ),  the  female  simplex 
(ZW),  and  consequently  the  chromosome-dislocation  hypothesis  must 
be  worked  out  contrawise  in  birds  and  insects.  We  should  have  to 
suppose  that  such  birds  start  as  males  (ZZ),  and  that  at  some  division 
of  the  cells  of  the  embroyo  one  of  the  Z's  became  lost  (left  at  the  cell- 
wall  for  example).  All  the  cells  that  got  ZZ  would  be  male ;  all  that  got 
Z  would  be  female.  If  the  reproductive  region  included  cells  of  these 
two  kinds,  an  ovotestis  would  result.  The  rest  of  the  body  should  be 
the  same,  or  nearly  so,  since  the  soma  of  male  and  female  birds  is  alike 
whether  ZZ  or  Z,  except  in  so  far  as  it  is  affected  by  the  secretions  from 
the  ovaries  (in  most  races  of  poultry),  or  from  the  testes  if  the  race 
be  Sebright,  Campines,  or  Hamburgs.  Birds  with  ovotestis  might, 
nevertheless,  be  expected,  on  this  view,  to  show  at  times  an  inter- 
mediate condition  of  the  secondary  sexual  characters,  according  to 
how  much  internal  secretion  is  produced  in  the  ovotestis.  In  other 
words,  the  chromosome  loss  might  involve  much  more  extensive 
regions  than  the  reproduction  organs,  but  show  its  effects  first  in  that 
organ  and  then  indirectly  other  parts  of  the  body  be  affected  by  the 
luteal  cells  of  the  testis.  There  is  one  rather  good  piece  of  evidence 
that  seems  opposed  to  this  interpretation.  In  the  hermophroditea  the 
oviduct  is  present  in  all  cases.  Its  conspicuous  presence  in  the  four 
hermaphrodites   would   seem,  therefore,  to   indicate   that   the   birds 


42  THE    GENETIC   AND   THE    OPERATIVE   EVIDENCE 

started  as  females  (ZW),  which  is  inconsistent  with  the  dislocation 
hypothesis.  The  alternate  would  be  that  in  all  these  cases  the  Z  part 
always  included  the  region  of  the  oviduct,  which  seems  improbable. 

There  is  another  possibility,  viz,  that  in  birds  a  sex-factor  is  carried 
by  the  W  chromosome,  and  ZW  is  a  female  not  because  of  one  Z,  but 
due  to  the  presence  of  W.  If  so,  then  one  Z  or  two  Z's  might  give  the 
same  result,  viz,  female.  If  a  bird  started  as  female,  (ZW)  and  chromo- 
somal dislocation  occurred,  then  the  Z  parts  would  be  female  and  the 
male  part  W.  Until  we  get  evidence  on  this  point  it  is  not  worth 
elaborating.  Without  genetic  evidence  from  hybrids,  the  interpretation 
of  hermaphrodites  in  birds  can  have  at  present  only  a  speculative 
interest.  We  may  hope  some  day  to  get  the  same  kind  of  evidence 
as  in  the  case  of  Drosophila.  Hermophrodite  hybrid  pheasants  that 
have  been  often  described  might  seem  to  furnish  a  hopeful  field,  for 
they  appear  to  be  quite  common  and  to  show  characteristics  of  both 
races.  As  yet,  however,  no  one  has,  I  think,  succeeded  in  finding  a 
simple  interpretation  of  the  results.  It  is  also  not  unlikely  that  many 
of  the  pheasant  cases  are  not  true  hermaphrodites,  but  due  to  failure 
of  normal  development  of  the  reproductive  gland,  which  gives  an 
intermediate  or  mixed  type  of  secondary  sexual  characters. 


RELATING   TO   SECONDARY   SEXUAL   CHARACTERS.  43 

PART  II. 

DARWIN'S  THEORY  OF  SEXUAL  SELECTION. 

Darwin  seems  to  have  felt  the  necessity  of  giving  some  other  explana- 
tion for  the  secondary  sexual  differences  between  the  male  and  female 
than  that  such  differences  were  only  a  by-product  or  concomitant  of 
sex  itself.  His  reason  for  searching  further  was  probably  a  part  of  the 
general  point  of  view  he  had  reached  in  regard  to  the  utility  of  special 
structures  of  animals,  namely,  that  their  presence  finds  its  explanation 
on  the  basis  of  utility.  Believing  as  he  did  that  most  of  the  adaptat  ions 
of  plants  and  animals  have  been  built  up  by  the  accumulation  of  small 
steps,  it  must  have  appeared  to  Darwin  inconceivable  that  the  highly 
developed  ornamentation  exhibited  in  the  secondary  sexual  characters 
could  have  been  simply  the  by-product  of  sex  itself,  especially  when 
the  ornamentation  may  have  been  entirely  absent  in  males  of  closely 
related  species.  To-day  we  are  not,  I  think,  so  oppressed  with  the 
difficulties  of  the  situation,  for  we  have  become  familiar  with  the  fact 
that  very  slight  genetic  differences  may  cause  very  great  differences 
in  the  end-product.  In  a -word,  the  problem  seems  less  formidable  to 
us  than  it  did  to  Darwin. 

Darwin  appealed  to  three  processes  to  account  for  the  facts:  (1)  to 
natural  selection  between  the  members  of  the  same  sex;  (2)  to  choice 
on  the  part  of  the  "other"  sex;  (3)  to  the  " inheritance  of  use."  Since 
each  of  these  appeals  to  a  different  procedure,  let  us  take  them  up 
separately. 

Competition  of  the  males  with  each  other  for  the  female  would, 
Darwin  said,  lead  to  the  survival  of  those  males  best  endowed  with 
organs  of  offense  and  defense.  The  spurs  of  the  cock  are  weapons  dan- 
gerous for  other  birds;  the  horns  of  the  bull  and  those  of  deer  are  used 
for  offense  and  defense;  the  mane  of  the  lion  is  a  protection  against  the 
teeth  of  other  lions.  It  is  true  that  these  same  weapons  and  shields 
serve  for  attack  and  defense  outside  the  species;  but  since  the  female 
lacks  them  or  has  them  less  developed,  they  would  not  seem  necessary 
for  survival  of  the  individual  against  aggression  from  without.  They 
have  developed,  then,  through  competition  within  the  specie-. 

Several  objections  of  greater  or  less  weight  have  been  urged  against 
Darwin's  interpretation.  It  has  been  pointed  out  that  the  combats 
within  the  species  are  seldom  fatal  and  that  the  defeated  rival  finds 
another  mate.  If,  as  a  rule,  there  are  as  many  females  as  males  within 
the  species  and  monogamy  is  the  rule,  all  males  will  find  partners 
sooner  or  later,  all  may  have  offspring,  and  the  offspring  have  squally 
good  chances  of  survival.  Under  these  circumstances  it  is  not  to  be 
expected  that  the  combat  would  be  likely  to  lead  to  the  production  of 
males  with  longer  spurs  or  larger  horns. 


44  THE    GENETIC   AND   THE    OPERATIVE   EVIDENCE 

Darwin  realized  this  difficulty  and  tried  to  meet  it  by  another 
assumption,  viz,  that  the  better  endowed  males  would  also  be  more 
likely  to  have  more  offspring.  How  could  this  be  made  probable? 
Darwin  suggested  that  the  strongest  males  would  be  in  position  to 
mate  with  the  first  females  to  reach  maturity,  and  if  these  were  more 
likely  to  have  offspring,  either  because  of  maternal  endowments  that 
made  them  also  more  prolific  or  because  the  earlier  broods  would  have 
a  better  chance  of  getting  food,  etc.,  then  the  successful  competitor 
would  sooner  or  later  impress  his  advantages  on  the  race. 

At  other  times  Darwin  suggested  that  the  exceptional  vigor  that 
led  to  the  greater  development  of  the  character  in  question  would 
itself  be  of  value  and  through  transmission  to  the  offspring  lead  to 
advance  in  the  development  of  the  other  character  in  question.  But 
here  the  argument  shifts  to  another  field  of  inquiry  and  survival  is 
ascribed  to  greater  vigor,  while  the  secondary  sexual  character  is  carried 
along  in  its  wake  as  a  sort  of  correlated  effect. 

It  will  be  conceded,  I  think,  that  such  pleading  does  not  help  the 
argument,  but  exposes  rather  its  inherent  weaknesses.  There  is, 
however,  a  line  of  defense  that  is  permissible.  If  monogamy  is  not  the 
rule,  if  the  male  captures  or  attracts  several  females  and  keeps  a  harem, 
as  do  the  fur  seals  and  walruses,  or  rules  a  herd  as  does  the  bull,  or  has 
a  flock  as  does  the  cock,  or  mates  more  frequently  with  random  females 
than  do  some  other  males,  then  the  advantage  of  his  more  developed 
weapon  might  lead  to  more  offspring.  If  it  could  be  shown  that  such 
intraspecific  weapons  prevail  more  frequently  within  polygamous  spe- 
cies, a  fair  argument  for  natural  selection  might  be  made.  I  do  not  know 
whether  such  a  census  has  been  taken  as  yet,  but  it  is  true,  I  think, 
that  in  most  polygamous  groups  we  find  weapons  of  offense  very  highly 
developed.  The  fur  seal  has  a  harem  and  the  male  is  greater  in  size, 
in  strength,  and  in  the  development  of  his  tusks  than  is  the  female. 
Similarly  for  the  walrus.  The  bull  drives  away  rival  bulls  from  the 
herd  until  through  age  or  injury,  or  through  the  development  of  a 
better  fighter,  he  is  replaced.  If  the  better  endowment  is  due  to  a 
genetic  factor,  we  should  expect  natural  selection  to  keep  the  race  at 
the  highest  possible  level  that  variation  supplies  material  for.  If,  then, 
we  confine  the  application  of  natural  selection  to  cases  of  this  sort,  the 
explanation  is  as  valid  as  is  the  theory  in  other  fields.  Such  a  con- 
clusion becomes  weakened  when  an  attempt  is  made  to  apply  it  to 
other  groups  of  animals  in  which  it  appears  improbable  that  the 
secondary  sexual  characters  of  the  male  have  any  obvious  value  as 
organs  of  offense.  There  are  families  of  beetles,  for  example,  in  which 
the  development  of  the  horns  of  the  male  are  as  striking  as  are  those  of 
the  ram  or  the  stag.  The  males  of  these  beetles  are  not  known  to  fight 
with  each  other,  nor  are  they  polygamous.  It  may  seem  that  we  must 
look  here  for  some  other  explanation,  which,  if  found,  might  suffice  to 


RELATING   TO    SECONDARY    SEXUAL    CHARACTERS.  45 

cover  also  the  case  of  birds  and  mammals.  In  answer  to  this  criti- 
cism it  may  be  argued  that  it  is  also  possible  that  the  other  explana- 
tion when  found  need  not  necessarily  apply  to  the  higher  animals, 
where  the  laws  of  combat  may  still  give  the  true  explanation.  On  the 
whole,  I  think  that,  for  our  present  purpose,  it  will  suffice  to  state 
it  is  consistent  with  the  theory  of  natural  selection  to  accept  prorision- 
ally  this  part  of  Darwin's  theory  for  those  species  in  the  higher  groups 
in  which  polygamy  holds,  conceding,  however,  that  even  here  it  may 
have  to  be  altered  when  fuller  knowledge  is  gained. 

We  are  more  concerned  with  that  special  feature  of  Darwin's  theory 
of  sexual  selection  that  is  applied  to  those  cases  where  the  characters 
are  supposed  to  owe  their  special  development  to  selection  by  the 
individuals  of  the  opposite  sex.  It  is  assumed  that  the  female  chooses 
the  better  endowed  males,  because  of  the  strong  appeal  he  makes  to 
her  sense-organs.  Here  we  must  employ  perforce  or  for  brevity's  sake 
the  terms  used  in  human  psychology,  and  run  the  risk  at  every  turn  of 
imputing  to  other  animals  the  emotions  and  acquired  associations 
which  man  himself  utilizes.  Even  granting  that  other  animals  pos- 
sess somewhat  similar  emotions  to  ours,  there  still  remains  always  the 
danger,  in  the  absence  of  real  evidence,  of  imputing  to  them  the  par- 
ticular emotion  that  we  call  "feeling  for  beauty";  and  the  greater 
danger  of  imputing  an  esthetic  sense  so  highly  developed  that  the  choice 
falls  in  the  long  run  on  the  suitor  better  ornamented  than  his  rivals. 

OTHER  THEORIES  TO  ACCOUNT  FOR  SECONDARY  SEXUAL 

CHARACTERS. 

Wallace  has  always  been  an  opponent  of  Darwin's  theory  of  sexual 
selection  in  so  far  as  it  is  based  on  female  choice.  As  already  stated, 
he  believes  that  the  difference  between  the  plumage  of  the  male  and 
female  in  birds  is  due  to  natural  selection  keeping  down  the  ornamen- 
tation and  high  coloration  in  the  female,  because  these  would  be 
expected  to  expose  the  female  while  sitting  on  the  nest  to  the  attacks 
of  enemies,  more  especially  of  hawks.  In  support  of  this  view  he 
points  to  a  long  series  of  species  which  build  exposed  nests  and  in  them 
the  female  is  plainly  and  inconspicuously  colored,  while  he  also  points 
out  that  in  such  birds  as  parrots,  toucans,  woodpeckers,  hangnests, 
and  starlings,  which  nest  in  holes  or  have  covered  nests,  the  female 
is  often  as  highly  colored  as  the  male.  It  can  not  be  denied  that 
he  makes  out  rather  a  strong  case  in  support  of  this  view,  despite  the 
fact  that  there  are  other  birds,  like  the  Baltimore  oriole,  that  have 
covered  nests  and  in  which  the  sexes  are  very  markedly  different. 

Wallace  tries  to  meet  cases  like  the  last  one  by  assuming  that  the 
covering  keeps  off  the  rain ;  but,  if  so,  why  are  the  sexes  st  ills.,  different  ? 
In  the  case  of  other  highly  colored  birds,  such  as  jays,  magpies,  hawks. 
and  crows,  Wallace  believes  that  these  birds  are  all  aggressive,  hence 


46       THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

can  protect  their  nests  if  attacked.  As  a  further  support  of  his 
view,  Wallace  points  out  that  in  the  few  cases  where  the  female  is 
more  highly  colored  than  the  male  (as  the  dotterel,  species  of  phalarope, 
an  Australian  creeper)  the  male  incubates  the  eggs. 

Wallace's  suggestion  still  leaves  unexplained  the  ornamentation  of 
the  male,  which  he  tries  to  account  for  as  the  direct  result  of  the  greater 
vitality  of  the  male.  He  tries  to  show  that  excessive  ornaments  and 
high  coloration  develop  especially  in  those  parts  of  the  body  to  which 
there  is  an  unusual  supply  of  blood  or  where  nerves  and  blood-vessels 
emerge  to  go  to  the  skin  or  to  the  muscles. 

"If  we  have  found  a  vera  causa  for  the  origin  of  ornamental  appendages  of 
birds  and  other  animals  in  a  surplus  of  vital  energy,  leading  to  abnormal 
growths  in  those  parts  of  the  integument  where  muscular  and  nervous  action 
are  greatest,  the  continuous  development  of  these  appendages  will  result  from 
the  ordinary  action  of  natural  selection  in  preserving  the  most  healthy  and 
vigorous  individuals,  and  the  still  further  selective  agency  of  sexual  struggle 
in  giving  to  the  very  strongest  and  most  energetic  the  parentage  of  the  next 
generation.  And,  as  all  the  evidence  goes  to  show  that,  so  far  as  female  birds 
exercise  any  choice,  it  is  for  'the  most  vigorous,  defiant,  and  mettlesome  male/ 
this  form  of  sexual  selection  will  act  in  the  same  direction,  and  help  to  carry 
on  the  process  of  plume  development  to  its  culmination.  That  culmination 
will  be  reached  when  the  excessive  length  or  abundance  of  the  plumes  begins 
to  be  injurious  to  the  bearer  of  them;  and  it  may  be  this  check  to  the  further 
lengthening  of  the  peacock's  train  that  has  led  to  the  broadening  of  the 
feathers  at  the  ends,  and  the  consequent  production  of  the  magnificent  eye- 
spots  which  now  form  its  crowning  ornament. 

"The  display  of  these  plumes  will  result  from  the  same  causes  which  led  to 
their  production.  Just  in  proportion  as  the  feathers  themselves  increased  in 
length  and  abundance,  the  skin-muscles  which  serve  to  elevate  them  would 
increase  also;  and  the  nervous  development  as  well  as  the  supply  of  blood  to 
these  parts  being  at  a  maximum,  the  erection  of  the  plumes  would  become  a 
habit  at  all  periods  of  nervous  or  sexual  excitement.  The  display  of  the 
plumes,  like  the  existence  of  the  plumes  themselves,  would  be  the  chief  external 
indication  of  the  maturity  and  vigor  of  the  male,  and  would,  therefore,  be 
necessarily  attractive  to  the  female.  We  have,  thus,  no  reason  for  imputing 
to  her  any  of  those  esthetic  emotions  which  are  excited  in  us,  by  the  beauty  of 
form,  color,  and  pattern  of  these  plumes;  or  the  still  more  improbable  esthetic 
tastes,  which  would  cause  her  to  choose  her  mate  on  account  of  minute  differ- 
ences in  their  forms,  colors,  or  patterns." 

Wallace  says,  referring  to  the  immense  tuft  of  golden  plumage  in 
the  best  known  birds  of  paradise  (Paradisea  apoda  and  P.  minor)  that 
springs  from  a  very  small  area  on  the  side  of  the  breast,  that  Mr.  Frank 
E.  Beddard,  who  has  kindly  examined  a  specimen,  says  that  "this 
area  lies  upon  the  pectoral  muscles,  and  near  to  the  point  where  the 
fibers  of  the  muscle  converge  towards  their  attachment  to  the  humerus. 
The  plumes  arise,  therefore,  close  to  the  most  powerful  muscle  of  the 
body,  and  near  to  where  the  activities  of  that  muscle  would  be  at  a 
maximum.    Furthermore,  the  area  of  attachment  of  the  plumes  is  just 


RELATING    TO    SECONDARY    SEXUAL    CHARACTERS.  47 

above  the  point  where  the  arteries  and  nerves  for  the  supply  of  the 
pectoral  muscles,  and  neighboring  regions,  leave  the  interior  of  the 
body.  The  area  of  attachment  of  the  plume  is,  also,  as  you  say  in  your 
letter,  just  above  the  junction  of  the  coracoid  and  sternum."  "  Orna- 
mental plumes  of  considerable  size  rise  from  the  same  part  in  many 
other  species  of  paradise  birds,  sometimes  extending  laterally  in  front, 
so  as  to  form  breast  shields.  They  also  occur  in  many  hummingbird-, 
and  in  some  sun  birds  and  honey-suckers;  and  in  all  these  cases  there 
is  a  wonderful  amount  of  activity  and  rapid  movement,  indicating 
a  surplus  of  vitality,  which  is  able  to  manifest  itself  in  the  development 
of  these  accessory  plumes."1 

There  are  two  serious  defects  in  such  an  attempt  to  explain  the  facts. 
In  the  first  place,  it  has  been  shown  in  several  cases  that  have  been 
studied  that  it  is  not  the  lessened  "vitality"  of  the  female  but  thesuppres- 
sion  caused  by  the  ovary  that  keeps  down  the  development  of  the  full 
plumage  in  that  sex.  In  the  second  place,  the  anatomical  influences 
appealed  to  are  imaginary  rather  than  real,  for  it  is  by  no  means 
apparent  that  the  local  exits  of  blood-vessels  and  nerves  to  muscle- 
are  at  all  correlated  with  the  location  of  the  ornamental  parts,  in  the 
skin.  Even  when  larger  blood-vessels  run  to  the  region  of  excessive 
development  of  feather  ornaments  it  may  well  be  that  they  go  there 
because  the  ornaments  in  question  use  them  for  their  nourishment;  in 
other  words,  Wallace  puts  the  cart  before  the  horse.  The  top  of  the  head . 
where  crests  so  often  develop,  the  throat  coloration  and  throat  shields 
of  hummingbirds  and  birds  of  paradise,  the  two  long  tail  feathers  of 
several  species  of  hummingbirds,  etc.,  do  not  arise,  so  far  as  known, 
from  regions  which  are  conspicuous  for  a  rich  supply  of  blood  and 
nerves.  Wallace's  appeal  to  underlying  organs  such  as  muscles  that 
supposedly  influence  the  special  development  of  the  feathers  in  the 
skin  above  does  not  strike  one  as  a  fortunate  appeal  to  physiological 
principles. 

Hudson,  in  his  interesting  book,  "The  Naturalist  in  La  Plata,"  has 
also  criticized  Darwin's  theory  of  sexual  selection.  He  has  brought 
together  a  considerable  number  of  interesting  observations  that  go  to 
show  that  the  displays — dancing,  singing,  and  combats — of  males  and 
females  have  no  relation  to  mating.  Many  of  them  involve  birds 
already  mated,  sometimes  several  males  participating,  sometimes 
males  and  females  together.  Some  of  the  tourneys  he  describes  are 
more  elaborate  than  the  mating  instincts  themselves,  yet  arc  not  con- 
cerned with  mating.  He  attempts  to  explain  them  as  overflow  phe- 
nomena, i.  e.,  as  expressions  of  the  high  vitality  of  the  males,  especially 
at  this  time.  If  he  is  right,  then  elaborate  exhibitions  of  these  kind- 
have  evolved  that  have  no  special  connection  with  mating.     Are  we 

1  For  activity  and  pugnacity  in  hummincliinls,  ne Tropical  Nature,  pp.  ISC,  MS. 


48       THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

called  upon  for  a  different  explanation  for  other  differences  that  dis- 
tinguish the  sexes?  One  example  will  suffice  to  bring  out  a  curious 
emotional  (?)  display  that,  elaborate  as  it  is,  has  no  apparent  connec- 
tion with  mating  (p.  269) : 

"The  lapwing  display,  called  by  the  natives  its  'dance'  or  'serious  dance' — 
by  which  they  mean  square  dance — requires  three  birds  for  its  performance, 
and  is,  so  far  as  I  know,  unique  in  this  respect.  The  birds  are  so  fond  of  it 
that  they  indulge  in  it  all  the  year  round,  and  at  frequent  intervals  during  the 
day,  also  on  moonlight  nights.  If  a  person  watches  any  two  birds  for  some 
time — for  they  live  in  pairs — he  will  see  another  lapwing,  one  of  a  neighboring 
couple,  rise  up  and  fly  to  them,  leaving  his  own  mate  to  guard  their  chosen 
ground ;  and  instead  of  resenting  this  visit  as  an  unwarranted  intrusion  on  their 
domain,  as  they  would  certainly  resent  the  approach  of  almost  any  other  bird, 
they  welcome  it  with  notes  and  signs  of  pleasure.  Advancing  to  the  visitor, 
they  place  themselves  behind  it;  then  all  three,  keeping  step,  begin  a  rapid 
march,  uttering  resonant  drumming  notes  in  time  with  their  movements ;  the 
notes  of  the  pair  behind  being  emitted  in  a  stream,  like  a  drumroll,  while  the 
leader  utters  loud  single  notes  at  regular  intervals.  The  march  ceases;  the 
leader  elevates  his  wings  and  stands  erect  and  motionless,  still  uttering  loud 
notes;  while  the  other  two,  with  puffed-out  plumage  and  standing  exactly 
abreast,  stoop  forward  and  downward  until  the  tips  of  their  beaks  touch  the 
ground,  and  sinking  their  rythmical  voices  to  a  murmur  remain  for  some  time 
in  this  posture.  The  performance  is  then  over  and  the  visitor  goes  back  to 
his  own  ground  and  mate,  to  receive  a  visitor  himself  later  on."1 

Cunningham,  who  has  brought  together  many  interesting  cases  of 
secondary  sexual  differences  in  his  book  on  "Sexual  Dimorphism  in  the 
Animal  Kingdom,"  attempts  to  show  that  the  development  of  the 
secondary  sexual  characters  of  the  males  are  due  directly  to  the  use  of 
certain  parts  of  the  body  during  courtship — the  use  of  the  parts  leading 
to  the  enlargement  and  excessive  growth  of  the  parts.  The  effects 
are  believed  by  him  to  be  inherited,  and  he  tries,  furthermore,  to  show  the 
way  in  which  such  acquired  characters  could  be  inherited.  He  makes 
use  of  the  modern  idea  of  hormones — substances  that  are  elaborated 
in  many  organs  of  the  body,  whose  effects  are  often  most  conspicuously 
produced  in  other  parts  of  the  body.  He  imagines  these  hormones  to 
be  collected  in  the  germ-cells  and  transmitted  to  the  next  generation, 
where  their  presence  contributes  to  the  further  development  of  the 
special  region  (when  it  develops)  that  corresponds  to  the  region  in 
its  parent  in  which  the  hormone  was  made.  His  speculation  meets 
in  the  first  place  with  the  general  objections  inherent  in  Lamarck's 
theory — objections  so  well  recognized  to-day  that  I  need  not  go  over 
them  here.  His  special  appeal  to  the  hormone  theory  makes  use  of  that 
theory  in  a  way  to  which  it  was  never  intended  to  be  put,  by  assuming 
that  an  internal  secretion  formed  in  one  organ  can  be  stored  up  in 
another  organ,  eggs  and  sperm — an  assumption  not  only  unsupported 
by  any  evidence,  but,  as  I  have  stated,  one  quite  foreign  to  the  hor- 

1  The  Naturalist  in  La  Plata,  W.  H.  Hudson,  London,  1892,  pp.  269-270. 


RELATING    TO    SECONDARY    SEXUAL    CHARACTERS.  49 

mone  theory.  In  fact,  Cunningham's  suggestion  is  nothing  more  than 
Darwin's  old  idea  of  pangens,  which,  being  imaginary,  could  be  en- 
dowed with  all  desirable  properties.  But  one  can  not  invoke  a  chemi- 
cal substance,  even  a  hormone,  and  then  at  the  critical  moment  endow 
it  with  special  virtues. 

A  rather  unique  explanation  of  the  origin  of  secondary  sexual  charac- 
ters is  made  by  Stolzmann.  His  argument  runs  as  follows:  (1)  There  is 
a  great  excess  of  males  in  birds;  (2)  the  males  left  over  after  mating 
are  useless  to  the  species,  since  they  can  not  propagate  and  they  con- 
sume food  needed  by  the  reproducing  part  of  the  population ;  (3)  the 
conspicuous  coloration  of  the  male  has  been  evolved  in  order  that  he 
could  be  seen  more  readily  by  birds  of  prey  and  the  objectionable 
excess  of  males  removed;  the  comb  of  the  cock  has  developed  in  order 
that  he  may  be  the  more  easily  killed  by  other  cocks. 

Stolzmann's  account  of  the  origin  of  the  plumes  of  the  birds  of 
paradise  should  be  immortalized  in  the  literature  of  the  subject: 

"Nous  comprendrons  aussi  facilement  la  presence  de  longues  plumos  chez 
les  males  de  nombreuses  especes,  comme  p.  e.  chez  les  oiseaux  de  paradis,  chez 
les  veuves  (Vidua)  et  chez  l'engoulevent  africain  (Cosmetornis).  Telles 
plumes  ont  probablement  pour  but  de  relantir  le  vol  des  males.  J'ai  constat*- 
chez  la  Loddigesia  mirabilis  (oiseaumouche  pe>uvien),  que  le  view  male 
poss£de  l'aile  quelques  millimetres  plus  courte  que  le  jeune  male  ou  la  femelle. 
Cet  avortement  des  remiges  provient  assurement  a  cause  de  deVeloppement 
extraordinaire  de  retrices  externes  chez  le  vieux  male  de  cet  oiseaumouche. 
Si  done  d'une  part  les  retrices  allongees  rendent  le  vol  plus  difficile  et  d'hautre 
les  ailes  plus  petites  diminuent  sa  v61ocit6,  le  vol  du  male  doit  etre  plus  lent 
que  celui  de  la  femelle,  le  poids  du  corps  restant  la  meme.  Le  develop- 
pement  extraordinaire  soit  des  remiges  soit  des  rectrices,  en  relantissant  le 
vol  des  males,  rend  leur  role  plus  difficile,  en  facilitant  en  meme  temps  celui 
des  femelles.  Nous  pouvons  prendre  comme  exemple  le  Cosmetornis,  qui, 
comme  tous  les  engoulevents,  se  nourrit  d'insectes,  qu'il  attrape  au  vol.  (  hez 
cet  oiseau  quelques  plumes  des  ailes  se  developpent  extraordinairement  pendant 
l'epoque  de  reproduction,  en  retardant  visiblement  son  vol.  II  est  done  facile 
a  remarquer,  qu'alors  le  male,  ayant  les  mouvements  plus  lounls,  n'est  pas  en 
etat  de  se  procurer  la  meme  quantity  d'insectes  qu'auparavant ;  ainsi  done  la 
femelle  a  plus  de  chances  de  trouver  une  nourriture  plus  ahondante."  l 

Equally  worthy  of  perpetuation  is  Stolzmann's  explanation  of 
dancing  and  singing  birds : 

"Toutes  les  reunions  des  males,  leurs  danses  bizarres,  leur  chant,  enfin,  ne 
servent  pas  probablement  a  s6duire  les  femelles,  mais  pour  distrain"  les  males, 
ce  qui  rend  plus  faciles  les  besognes  maternelles  des  femelles  et  au  surplus  les 
protege  contre  l'assiduite  nuisible  des  c61ibataires.  Darwin  lui-meme  con- 
state le  fait,  qu'ordinairement  pendant  les  reunions  des  males,  quand 
derniers  sont  trop  occupes  par  le  combat  ou  la  danse.  la  femelle  B'echappe  awe 
un  d'eux  pour  copuler.  Ainsi  done  dans  ce  cas  e'est  bien  la  selection  D&turelle 
et  non  la  selection  sexuelle,  qui  agit  pour  la  conservation  d'equilibn  sexuel."  ■ 

Proceedings  of  the  Zoological  Society  of  London,  1885,  p.  431,  QMJqUM  IwaQMI  sur  le 
dimorphisme  sexuel.     Jean  Stolzmann. 


50       THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

DISPLAY  OF  THE  MALE. 

The  antics  of  male  birds  at  the  mating  season,  their  courtship 
so-called,  has  played  an  important  role  in  Darwin's  theory  of  sexual 
selection.  The  behavior  of  many  birds  at  this  time  is  of  such  a  kind  as 
to  suggest  that  the  male  is  exhibiting  his  plumage  before  the  female 
for  the  "purpose"  of  influencing  her  choice.  The  whole  parapher- 
nalia of  human  psychology  is  imported  into  the  situation  and  both  the 
consciousness  of  the  male,  his  intentions  so  to  speak,  and  the  supposed 
esthetic  response  or  choice  of  the  female  is  invoked.  Even  though  it 
be  granted  that  the  words  that  we  must  make  use  of,  borrowed  from 
human  behavior,  are  such  as  to  imply  much  more  in  the  direction  of 
consciousness  and  purpose  than  is  desirable,  and  that  most  of  the 
behavior  of  animals  should  be  stated  in  a  more  roundabout  and 
objective  way,  yet  the  theory  will  only  work  out  on  the  assumption 
that  the  female  chooses  in  some  sense  the  more  brilliant  or  ornamental 
(or  effective)  male,  whether  she  is  "conscious"  or  unconscious  of 
intention.  I  doubt  if  anyone  to-day  would  care  to  defend  seriously 
the  theory  on  the  grounds  of  consciousness  or  esthetic  value  of  the 
exhibition,  despite  the  fact  that  Darwin's  language  often  takes  this 
turn  and  the  less-guarded  statements  of  some  of  his  disciples,  such  as 
Romanes,  show  little  hesitation  in  anthropo-morphologizing  the  entire 
situation.  It  is,  however,  not  necessary  for  the  working  out  of  the 
theory  that  this  complication  be  introduced  into  it,  for  if  the  female 
is  more  likely  to  mate  with  a  more  brilliantly  colored  than  a  less 
brilliantly  colored  male,  the  theory  may  be  made  to  apply  regardless 
of  whether  she  is  "conscious"  or  not  of  the  difference  to  which  she 
responds. 

But  there  are  weighty  arguments  against  such  an  interpretation  of 
the  behavior  of  the  male  and  female  during  courtship.  In  the  first 
place,  there  is  almost  no  direct  evidence  to  show  that  the  female  mates 
with  the  more  ornamental  male.  As  this  is  the  all-essential  require- 
ment of  the  theory,  the  almost  complete  absence  of  facts  in  its  support 
leaves  the  theory  resting  on  a  theoretical  assumption.  It  can  scarcely 
pass  unnoticed  that  while  there  exists  a  large  mass  of  data  describing 
the  secondary  sexual  characters,  there  is  practically  nothing  in  this 
accumulation  to  show  that  the  female  makes  her  selection  on  differ- 
ences in  coloration  or  ornamentation.  And  on  the  other  hand,  there  is 
some  evidence  showing  that  the  female  is  ready  to  succumb  to  the 
aggressiveness  of  the  male  rather  than  that  she  "chooses"  him. 

The  behavior  of  the  male  under  sexual  excitement  is  often  described 
to  be  of  a  kind  to  exhibit  before  the  female  his  peculiar  adornments. 
That  the  "purpose"  of  his  exhibition  is  to  show  himself  off  before  the 
female  may  be  conceded,  with  reservations  as  to  what  is  meant  here 
by  "purpose."  That  the  male  is  conscious  of  the  probable  results  of  his 
conduct  is  scarcely  probable  the  first  time  he  courted ;  but  that  he  may 


RELATING   TO    SECONDARY    SEXUAL    CHARACTERS.  51 

have  found  out  the  most  probable  result  after  the  first  attempt  through 
"associative  memory"  is  in  accord  with  what  the  study  of  "animal 
behavior"  has  shown  to  be  possible.  In  this  sense  purpose  would  mean 
a  line  of  conduct  that  experience  had  shown  to  lead  to  a  certain  and. 
Anticipation  or  far-sightedness  would  henceforth  characterize  such  a 
reaction.  Here,  however,  we  venture  on  very  dubious  grounds.  Hut 
the  display  of  the  male  may  be  purposeful  in  a  much  simpler  sen.-*'. 
His  activity  may  be  an  inborn  reflex  to  visual  or  other  sensory  stimuli 
that  is  a  part  of  his  attack  on  the  female,  or  possibly  a  series  of  reflexes 
that  we  may  register  under  the  old  unanalyzed  terms  of  "desire  and 
fear."  The  action  calls  forth  a  responsive  reflex  in  the  female,  for 
the  sexual  act  is  not  entirely  active  on  one  side,  passive  on  the  other, 
but  consists  of  a  series  of  interreactions  on  the  part  of  each  sex,  which, 
if  they  pursue  a  given  course,  leads  to  the  final  mating.  The  mutual 
responses  appear  to  follow  an  automatic  course  in  many  cases  if  the 
individuals  are  sexually  ready  to  mate  and  the  environment  is  pro- 
pitious. Types  of  behavior  of  this  kind  must  be  familiar  to  anyone 
who  has  observed  domesticated  and  semi-domesticated  animals.  The 
purpose  of  the  display  may  mean  no  more  than  a  reaction  that  leads 
to  a  result  propitious  to  the  perpetuation  of  the  species  if  the  situation 
is  ripe  for  such  an  outcome. 

This  conclusion  still  leaves  open  the  question  as  to  whether  the 
display  is  more  likely  to  be  successful,  if  certain  special  characters 
possessed  by  the  species  are  exhibited.  In  the  absence  of  any  sufficient 
evidence  to  show  that  this  is  so,  and  in  the  light  of  the  very  great  danger 
of  projecting  "our  human  standards"  into  the  world  of  other  animals, 
and  in  view  of  the  fact  that  related  species  without  such  marks  are  as 
successful  in  maintaining  themselves,  I  can  not  but  think  that  at 
present  we  have  a  good  deal  to  lose  in  the  way  of  scientific  procedure 
and  nothing  to  gain  of  scientific  value  in  accepting  Darwin's  inter- 
pretation of  sexual  selection  based  on  the  display  of  the  male  as  fur- 
nishing an  opportunity  to  the  female  to  make  the  "best"  selection 
amongst  her  suitors  on  the  basis  of  his  adornment. 

An  excellent  opportunity  to  study  the  problem  as  to  "choosing" 
by  the  female  is  furnished  by  the  mutant  races  of  Drosophila.  BOOM 
of  which,  differing  in  a  single  mutant  gene,  have  wings  as  different  in 
coloration  as  black,  yellow,  or  gray,  and  eyes  as  differently  colored  as 
white,  vermilion,  or  red.  Sturtevant  put  a  yellow  female  with  a  gray 
(wild-type)  male  and  a  yellow  male.  The  male  that  Inst  mated  was 
noted  and  the  trio  discarded.  The  female  "chose"  the  gray  malec 
times  and  the  yellow  only  8  times.  In  the  control  combination,  when'  a 
gray  female  "chose"  between  the  same  two  kinds  of  males,  she  took 
the  gray  male  60  times  and  the  yellow  male  12  times.  In  both  cases  it 
"appears"  that  the  female  " prefers "  the  gray  male,  but  this  deduction 
may  give  an  entirely  wrong  impression  as  to  what  is  taking  place,  for 


52  THE    GENETIC   AND   THE    OPERATIVE   EVIDENCE 

the  result  would  be  the  same  in  kind  if  the  gray  male  were  more  active 
and  mated  quicker.  This  was  tested  by  putting  a  gray  and  a  yellow 
female  with  a  gray  male  and  then  for  control  a  gray  and  a  yellow  female 
with  a  yellow  male.    The  result  was  as  follows : 

RedcfJGray9 25  y  u  (Gray  9 12 

Ked  &  \Yellow  9 31  le  OW  ^  \Yellow  9 30 

Here  the  gray  male  mated  slightly  oftener  with  the  yellow  female 
than  with  the  other,  whereas  the  yellow  male  mated  much  oftener  with 
the  yellow  female  than  with  the  gray  one.  Both  results  are  explicable 
on  the  view  that  the  yellow  female,  being  less  active,  is  more  easily 
captured  by  the  yellow  male  than  is  the  gray  female.  This  view  fits 
in  also  with  the  former  experiment,  where  the  yellow  male  is  much  less 
successful  than  the  more  active  gray  male.  Such  a  conclusion  gives  a 
more  consistent  explanation  of  all  the  facts  than  does  the  theory  of 
female  choice,  for  on  the  latter  we  must  suppose  that  the  yellow 
females  prefer  the  gray  males  and  the  yellow  male  prefers  the  yellow 
females,  etc. 

The  following  results  were  obtained  by  Sturtevant  when  red  and 
white  eyed  flies  were  competing : 

„    ,    ,     /Red  9 54  p    .  „      /Red  61 53 

Redc?     \White  9 82  Red$     \Whitec? 14 

wuu    ^/Red9 40  w,;.     0  /Red  c? 62 

White  c?  (white  ? Q3  Wlute  ?   \White  cf 19 

The  outcome  can  be  interpreted  in  the  same  way  as  the  yellow-gray 
competition.  The  red  male  wins  by  virtue  of  his  greater  activity,  while 
the  white  female  is  chosen  more  often,  especially  by  the  white  male, 
because  of  her  passivity  (or  weaker  resistance) .  It  may  be  claimed  that 
these  results  do  not  show  that  the  female  does  not  choose,  for  such 
choice,  if  made,  would  be  swamped  by  another  condition  of  the  experi- 
ment, viz,  the  greater  aggressiveness  of  one  kind  of  male  and  greater 
passivity  of  the  other  kind  of  female.  This,  of  course,  is  true,  but  the 
experiment  still  shows  that  in  these  flies  other  influences  are  so  much 
greater  than  "choice"  by  the  female,  if  it  exists,  that  the  postulated 
effect  of  the  latter  practically  disappears  from  the  situation. 

Mayer's  experiments  with  the  large  moth  Callosamia  promethea 
furnish  important  information  as  to  the  factors  involved  in  mating. 
The  results  are  all  the  more  significant  from  our  present  point  of  view 
because  the  colors  of  male  and  female  are  in  this  species  markedly 
different.  The  wings  of  the  male  are  black,  those  of  the  female  reddish 
brown;  the  antennae  of  the  male  are  large  and  bushy,  those  of  the 
female  small  and  slender.  Mayer  found  that  the  males  are  attracted 
by  the  female  from  some  distance  when  the  latter  are  put  into  a  glass 
jar  covered  by  only  coarse  mosquito-netting,  but  if  the  same  jars  are 
turned  upside  down  the  males  are  unable  to  find  the  female.    Females 


RELATING   TO    SECONDARY   SEXUAL   CHARACTERS.  53 

concealed  in  loose  cotton  attracted  males.  Females  were  put  into  a 
box  with  an  open  chimney  at  one  end,  the  other  open  end  being  covered 
by  mosquito-netting.  A  current  of  air  blew  into  the  open  end  and  out  of 
the  chimney.  The  males  flew  to  the  end  of  the  chimney  from  which 
the  air  came  and  fluttered  about  in  the  neighborhood.  Males  are 
attracted  to  places  where  a  female  has  been  kept  even  several  hours 
after  her  removal.  The  male  finds  the  female  through  the  sense-organs 
in  his  antenna?,  for  a  male  whose  abdomen  has  been  cut  off  and  the  sides 
of  whose  thorax  are  covered  with  shellac  will  still  fly  to  the  female, 
but  if  his  antennae  be  coated  with  any  substance  he  no  longer  seeks  the 
female.  If  the  eyes  of  the  males  are  blackened  they  will  mate  with 
females  "in  the  normal  manner." 

Mayer  cut  off  the  wings  of  females  and  glued  male  wings  in  their 
places,  so  that  the  female  looked  like  a  male.  Males  readily  mated 
with  these  females.  The  wings  of  males  were  cut  off  and  female  wings 
glued  in  their  place.  Mating  occurred  "with  normal  frequency,  and 
I  was  unable  to  detect  that  the  female  displayed  any  unusual  aver- 
sion" to  such  males.  Males  with  female  wings  pass  unnoticed  by  other 
males. 

In  a  later  paper  (1901)  Mayer  and  Soule  describe  how,  when  the  wings 
of  the  male  were  painted  scarlet  or  green,  the  males  were  accepted 
as  readily  as  normals  in  competition  with  them.  Experiments  were  ata  i 
made  by  them  with  the  gipsy  moth.  Wingless  males  met  with  more 
"resistance"  from  the  female  than  do  normal  males,  but  when  the  eyee 
were  covered  the  wingless  males  succeeded  as  often  as  the  normal 
males,  but  the  number  of  observations  on  which  this  statement  is 
were  far  too  few  to  be  of  any  value,  and  there  are  several  other  obser- 
vations that  make  any  such  conclusion  from  the  evidence  highly 
uncertain. 

That  it  is  the  odor  of  the  females  that  attracts  the  male  can  not  be 
doubted.  It  might  still  be  claimed  that  the  female  chooses  amongst 
her  suitors  the  darkest  males,  but  the  evidence  gives  no  grounds  for 
inferring  such  a  choice,  and  since  she  will  even  accept  males  with 
female  wings  when  they  attempt  to  mate  with  her,  it  does  not  appar 
probable  that  the  color  of  the  male  is  a  factor  in  the  result,  or  at  least 
if  it  is,  then  it  must  be  entirely  subordinate  to  the  sense  of  smell  in 
finding  the  female  and  of  touch  after  he  arrives.  These  is  little  or 
nothing  in  the  behavior  of  these  moths,  or  in  that  of  the  silkworm 
moth,  according  to  Kellogg,  to  suggest  that  vision  plays  any  significant 
role  in  courtship. 

Concerning  the  genetic  situation  in  insects,  there  are  only  a  few  casrs 
that  have  been  studied.  The  most  instructive  are  those  in  which  more 
than  a  single  kind  of  male  exists  (two  or  three),  one  of  which  may  b* 
like  the  female,  the  other  quite  different.  The  best  worked  out  cases 
are  Papilio  memnon  and  P.  polytes.     De  Meijere  and  Punnett  have 


54  THE    GENETIC   AND   THE    OPERATIVE   EVIDENCE 

shown  from  the  breeding  data  that  it  is  possible  to  frame  an  explanation 
of  such  a  sort  that  the  aberrant  female  differs  from  the  female  resem- 
bling the  male  in  only  a  single  genetic  factor — one  not  sex-linked 
(i.  e.,  not  carried  by  an  X  chromosome),  but  autosomal.  The  gene 
would  be  of  such  a  sort  that  it  affects  the  female  only — producing  no 
visible  effect  on  the  male.  Such  a  conclusion,  if  established,  helps, 
theoretically  at  least,  toward  simplifying  the  situation  in  other  species, 
for  it  shows  that  genetic  factors  occur  whose  influence  is  on  one  sex 
alone;  hence  the  difference  between  the  male  and  one  type  of  female 
does  in  such  cases  result  from  a  single  gene  present  in  both  but  causing 
them  to  be  differently  colored.  There  would  be  no  need,  then,  to  assume 
that  the  difference  had  been  slowly  built  up  by  selection,  but  rather 
that  the  difference  arose  at  some  time  by  a  single  mutant  step.  The 
incorporation  of  the  step  in  the  species  would  then  follow  if  the  effect 
of  the  gene  were  useful  in  mating  or  if  it  had  some  other  primary 
significance  for  the  welfare  of  the  species,  the  different  effect  produced 
on  the  male  and  female  being  only  an  unimportant  by-product  of  its 
action.  On  the  other  hand,  it  should  be  emphasized  that  because  a 
single  factor  difference  between  the  two  kinds  of  females  will  explain  the 
genetic  results,  it  does  not  necessarily  follow  that  the  difference  did 
arise  as  a  single  mutation.  The  foregoing  argument  does  no  more 
than  imply  that  the  difference  in  question  may  have  arisen  in  this  way, 
and  if  so,  that  the  situation,  as  it  exists,  would  be  the  more  easily 
comprehended. 

In  insects  and  spiders,  where  dimorphism  is  as  marked  as  in  birds, 
the  mating  habits  have  been  studied  by  a  number  of  naturalists.  Here 
alou  there  are  nuinexuus  accounts  of  the  display  of  the  male  during 
courtship.  The  account  given  by  Dr.  and  Mrs.  Peckham  are  particu- 
larly detailed  and  call  for  careful  consideration  on  account  of  their 
well-recognized  accuracy  in  observational  work.  Moreover,  as  a 
result  of  their  observations,  along  with  those  of  Montgomery,  Petrunke- 
witsch,  and  others,  we  have  really  fuller  information  concerning  the 
courtship  of  spiders  than  of  birds  and  of  mammals. 

In  the  great  majority  of  species  where  the  sexes  are  different  the  male 
is  more  brightly  colored  or  more  ornamental.  For  example,  in  a  group 
such  as  the  Attidae  of  France,  where  both  sexes  are  known,  the  Peck- 
hams  state  that  in  26  cases  the  male  is  more  conspicuous  than  the 
female;  in  55  cases  the  sexes  are  alike,  or  if  they  differ  the  male  is  more 
conspicuous.  It  appears  that  in  other  genera  there  are  cases  where  the 
female  is  more  conspicuous  than  the  male.  The  Peckhams  state  that 
possibly  as  many  as  250  species  are  in  this  condition.  Those  females 
with  brighter  colors  than  the  males  are  usually  well  armed  by  strong 
spines.  When  very  young  they  are  like  the  males  and  begin  to  assume 
the  adult  form  and  color  when  they  are  a  quarter  to  a  third  grown. 
Whether  the  change  depends  on  changes  in  the  ovary  is  not  known. 


RELATING   TO    SECONDARY    SEXUAL    CHARACTERS.  ">."> 

The  mating  behavior  of  Saitispulex,a,  species  in  which  the  males 
and  females  are  much  alike,  is  described  by  the  Peckhams  as  follows: 

"On  May  24th  we  found  a  mature  female  and  placed  her  in  one  of  the  larger 
boxes,  and  the  next  day  we  put  a  male  in  with  her.  He  saw  her  as  she  stood 
perfectly  still,  twelve  inches  away;  the  glance  seemed  to  excite  him  and  lie  at 
once  moved  toward  her;  when  some  four  inches  from  her  he  stood  still  and 
then  began  the  most  remarkable  performances  that  an  amorous  male  could 
offer  to  an  admiring  female.  She  eyed  him  eagerly,  changing  her  position 
from  time  to  time  so  that  he  might  be  always  in  view.  He,  raising  his  whole 
body  on  one  side  by  straightening  out  the  legs,  and  lowering  it  on  the  other  by 
folding  the  first  two  pairs  of  legs  up  and  under,  leaned  so  far  over  as  to  be  in 
danger  of  losing  his  balance,  which  he  only  maintained  by  sidling  rapidly 
toward  the  lowered  side.  The  palpus,  too,  on  this  side  was  turned  back  to 
correspond  to  the  direction  of  the  legs  nearest  it.  (Fig.  13.)  He  moved  in  a 
semi-circle  for  about  two  inches  and  then  instantly  reversed  the  position  of  the 
legs  and  circled  in  the  opposite  direction,  gradually  approaching  nearer  ami 
nearer  to  the  female.  Now  she  dashes  toward  him,  while  he,  raising  his  first 
pair  of  legs,  extends  them  upward  and  forward  as  if  to  hold  her  off,  but  withal 
slowly  retreats.  Again  and  again  he  circles  from  side  to  side,  she  gazing 
toward  him  in  a  softer  mood,  evidently  admiring  the  grace  of  his  antics.  This 
is  repeated  until  we  have  counted  111  circles  made  by  the  ardent  little  male. 
Now  he  approaches  nearer  and  nearer  and  when  almost  within  reach  whirls 
madly  around  and  around  her,  she  joining  and  whirling  with  him  in  a  giddy 
maze.  Again  he  falls  back  and  resumes  his  semi-circular  motions,  with  his 
body  tilted  over;  she,  all  excitement,  lowers  her  head  and  raises  her  body  ><> 
that  it  is  almost  vertical;  both  draw  nearer;  she  moves  slowly  under  him,  he 
crawling  over  her  head,  and  the  mating  is  accomplished. 

"After  they  have  paired  once,  the  preliminary  courtship  is  not  so  long. 
When  this  same  pair  mated  a  second  time,  there  was  no  whirling  movement, 
nor  did  the  female  lift  her  body,  as  at  first."     (pp.  37-38). l 

The  courtship  of  another  species,  Dendryphantes  capitatus,  in  which 
the  sexes  are  entirely  different,  is  described  as  follows : 

"The  males  of  capitatus  are  very  quarrelsome,  sparring  whenever  they  meet, 
chasing  each  other  about,  and  sometimes  clinching.  It  is  a  very  abundant 
spider  with  us,  so  that  we  often  put  eight  or  ten  males  into  a  box  to  sec  them 
fight.  It  seemed  cruel  sport  at  first,  but  it  was  soon  apparent  that  they  wen- 
very  prudent  little  fellows,  and  were  fully  conscious  that  'he  who  tights  and 
runs  away  will  live  to  fight  another  day.'  In  fact,  after  two  weeks  of  hard 
fighting  we  were  unable  to  discover  one  wounded  warrior.  When  the  males 
are  approaching  each  other,  they  hold  the  first  legs  up  in  a  vertical  direction. 
Sometimes  they  drop  the  body  on  to  one  side  as  they  jump  about  each  other. 
These  movement  are  very  quick,  and  they  are  always  ready  for  a  passage  at 
arms.  When  courting  the  females  they  have  another  movement.  They 
approach  her  rapidly  until  within  two  to  five  inches,  when  they  stop  and  extend 
the  first  legs  directly  forward,  close  to  the  ground,  the  legs  being  slightly 
curved  with  the  tips  turned  up.  (Fig.  18).  Whether  it  be  intentional  or  not . 
this  position  serves  admirably  to  expose  the  whole  of  the  bronze  and  white 
face  to  the  attentive  female,  who  watches  him  closely  from  a  little  distance 
(Fig.  19.)  The  males  also  give  their  palpi  a  circular  movement,  much  as  a 
person  does  when  washing  his  hands.     As  he  grows  more  excited,  he  lies  down 

1  George  W.  and  Elizabeth  G.  Pcckham.     Observations  on  Sexual  Si-lection  in  Bpfckn  of  the 
Family  Attidffi.     Nat.  Hist.  Soc.  of  Wisconsin,  Vol.  I,  1KS9,  pp.  46,  47. 


56       THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

on  one  side  with  his  legs  still  extended.  These  antics  are  repeated  for  a  very- 
long  time,  often  for  hours,  when  at  last  the  female,  either  won  by  his  beauty  or 
worn  out  by  his  persistence,  accepts  his  addresses."     (Pp.  45,  46.) 

In  another  species,  Dendryphantes  elegans,  both  sexes  are  brilliantly 
colored. 

"The  male  is  covered  with  iridescent  scales,  his  general  color  being  green; 
in  the  female  the  coloring  is  dark,  but  iridescent,  and  in  certain  lights  has  lovely 
rosy  tints.  In  the  sunlight  both  shine  with  the  metallic  splendor  of  humming- 
birds. The  male  alone  has  a  superciliary  fringe  of  hairs  on  either  side  of  his 
head,  his  first  legs  being  also  longer  and  more  adorned  than  those  of  his  mate. 
The  female  is  much  larger,  and  her  loveliness  is  accompanied  by  an  extreme 
irritability  of  temper  which  the  male  seems  to  regard  as  a  constant  menace  to 
his  safety,  but  his  eagerness  being  great,  and  his  manners  devoted  and  tender, 
he  gradually  overcomes  her  opposition.  Her  change  of  mood  is  only  brought 
about  after  much  patient  courting  on  his  part.  While  from  three  to  five 
inches  distant  from  her  he  begins  to  wave  his  plumy  first  legs  in  a  way  that 
reminds  one  of  a  wind-mill.  She  eyes  him  fiercely  and  he  keeps  at  a  proper 
distance  for  a  long  time.  If  he  comes  close  she  dashes  at  him  and  he  quickly 
retreats.  Sometimes  he  becomes  bolder  and  when  within  an  inch,  pauses, 
with  the  first  legs  outstretched  before  him,  not  raised  as  is  common  in  other 
species;  the  palpi  also  are  held  stiffly  out  in  front  with  the  points  together. 
Again  she  drives  him  off,  and  so  the  play  continues.  Now  the  male  grows 
excited  as  he  approaches  her,  and  while  still  several  inches  away  whirls  com- 
pletely around  and  around;  pausing,  he  runs  closer  and  begins  to  make  his 
abdomen  quiver  as  he  stands  on  tip-toe  in  front  of  her.  Prancing  from  side  to 
side,  he  grows  bolder  and  bolder,  while  she  seems  less  fierce,  and  yielding  to  the 
excitement  lifts  up  her  magnificently  iridescent  abdomen,  holding  it  at  one 
time  vertically  and  at  another  sideways  to  him.  She  no  longer  rushes  at  him, 
but  retreats  a  little  as  he  approaches.  At  last  he  comes  close  to  her,  lying  flat, 
with  his  first  legs  stretched  out  and  quivering.  With  the  tips  of  his  front  legs 
he  gently  pats  her;  this  seems  to  arouse  the  old  demon  of  resistance,  and  she 
drives  him  back.  Again  and  again  he  pats  her  with  a  caressing  movement, 
gradually  creeping  nearer  and  nearer,  which  she  now  permits  without  resis- 
tance until  he  crawls  over  her  head  to  her  abdomen,  far  enough  to  reach  the 
epigynum  with  his  palpus".     (Pp.  46-47.) 

If  we  lay  no  emphasis  on  the  implied  emotional  elements  in  the 
behavior  of  the  spiders  in  this  description — terms  of  emotion  borrowed 
direct  from  human  psychology — there  still  remain  the  several  types 
of  apparently  significant  reactions  associated  with  courtship.  The 
statements  leave  no  room  for  doubt  that  vision  plays  an  important 
role  in  the  complex  reflexes  that  lead  gradually  to  successful  mating. 
The  Peckhams  insist  that  the  display  of  the  male  is  always  of  a  kind 
to  bring  before  the  female  the  special  adornments  of  the  male  in  what- 
ever part  of  the  body  they  may  he.  The  chance  of  subjective  inter- 
pretation here  is  so  great  that  unless  the  results  are  carefully  checked 
up  by  studies  of  the  attitudes  assumed  by  males  in  species  in  which 
the  males  are  without  ornament,  their  interpretation  must  be  taken 
with  the  greatest  reserve.  Assigning,  as  our  authors  do,  so  much  by 
gratuitous  implication  to  the  emotional  side  of  the  picture  prejudices 


RELATING   TO   SECONDARY   SEXUAL   CHARACTERS.  57 

one,  perhaps  too  greatly,  against  accepting  a  special  (even  an  implied 
intentional)  exhibition  of  the  specially  ornamented  parts.  On  the 
other  hand,  if  it  be  conceded  that  the  conspicuousness  of  the  male  is 
an  element  in  the  reaction,  the  very  special  adornments  visible  from 
the  front  might  be  supposed  to  enhance  the  effect  produced  in  the 
female.  Similar  displays  of  special  ornamentation  in  the  male  have 
been  described  both  for  birds  and  insects,  but  here,  too,  the  question 
has  been  raised  as  to  whether  such  exhibitions  are  more  than  an 
accidental  accompaniment  of  the  posturing  of  the  male,  for  the  same 
kind  of  behavior  is  known  to  occur  in  other  cases  where  the  male  is 
unornamented  and  resembles  the  female.  Had  such  a  male  special 
ornamentation  it  would  no  doubt  appear  to  us  that  his  behavior  was 
"calculated"  to  display  his  ornaments. 

Dr.  and  Mrs.  Peckham  point  out  that  their  observations  are  entirely 
inconsistent  with  Wallace's  interpretation  of  the  origin  of  secondary 
sexual  characters.  They  find  no  evidence  in  favor  of  his  view  that  the 
male  possesses  greater  "vital  activity."  On  the  contrary,  the  female 
is  the  more  active  and  pugnacious  of  the  two.  They  also  object  to 
Wallace's  statement  of  a  total  absence  of  any  evidence  that  the  female 
notices  the  display  of  the  male.  In  spiders  the  females  "observe"  the 
males  with  close  attention  during  their  courtship.  They  point  out  also 
that,  in  spiders  at  least,  as  the  female  gradually  becomes  adult,  a  male 
if  preferred  will  have  a  chance  of  mating  with  several  females, "and 
as  the  mating  season  lasts  for  two  or  three  weeks  the  more  brilliant 
males  may  easily  be  selected  again  and  again."  In  regard  to  Wallace's 
argument  as  to  the  distribution  of  accessory  plumes  in  humming  birds, 
the  Peckhams  point  out  that — 

"The  pectoral  muscles  reach  their  highest  development  in  the  humming- 
birds, the  diurnal  birds  of  prey,  and  the  swallows,  and  wo  may,  therefore, 
fairly  use  these  groups  to  test  Mr.  Wallace's  explanation  of  breast  plumes.  In 
the  swallows  and  birds  of  prey  we  find  no  such  appendages,  in  spite  of  their 
further  claim  to  them,  on  the  ground  of  great  vigor  and  activity.  As  to  the 
humming-birds,  we  find  in  the  genus  Aglceactis  six  species  with  more  or  less 
developed  breast-plumes,  which  are  also  found  in  nine  other  species,  scattered 
through  different  genera — in  all,  only  fifteen  species  out  of  four  hundred  and 
twenty-six;  while  we  find  in  fifty-six  species  the  lengthened  and  modified  tail- 
feathers,  which,  according  to  Mr.  Wallace's  view,  should  be  peculiar  to  the 
Gallinacese. 

"Again,  there  are  elongated  feathers  from  the  throat  or  from  the  side  of  the 
neck  in  thirty-five  species,  while  seventeen  have  crests  from  the  top  of  the 
head,  and  seventeen,  downy  puffs  from  the  tarsi."  * 

From  this  brief  survey  of  the  family  we  see  that,  contrary  to  what 
we  should  expect  from  Mr.  Wallace's  theory,  although  the  breast 
muscles  are  the  seat  of  the  highest  activity,  breast  plumes  are  the  least 
frequent  of  all  the  forms  of  ornamental  plumage. 

1  Loddigesia  mirabilis  has  the  tail  about  three  times  as  long  as  the  body.     Similar  modifiwitiom 
are  found  in  the  genera  Sappho,  Cynanthus,  Lesbia,  Stegnura,  Di.icura.  OowWi'a,  ct  al. 


58  THE    GENETIC    AND    THE    OPERATIVE    EVIDENCE 

"We  may  fairly  say,  then,  that  the  humming-birds  completely  refute  the 
proposition  that  there  is  any  relation  between  the  development  of  color  and 
accessory  plumes  and  'surfaces  where  muscular  and  nervous  development  is 
considerable.'  m 

What  is  true  for  birds  is  even  more  obvious  for  spiders  where  the 
special  ornaments  are  not  confined  to  parts  of  the  body  with  high 
muscular  development,  etc.  The  writers  make  the  very  pertinent 
criticism  that  while  Wallace  objects  to  assuming  the  emotional  states 
in  females,  he  is  less  careful  in  regard  to  the  males'  emotions  when  he 
speaks  of  the  display  "under  the  influence  of  jealousy  or  sexual  excite- 
ment   The  males,  in  their  rivalry  with  each  other,  would  see 

what  plumes  were  most  effective;  and  each  would  endeavor  to  excel  his 
enemy  as  far  as  voluntary  exertion  would  enable  him."2 

"If  the  males  have  so  complex  an  emotion  as  jealousy,  and  further,  if  they 
are  conscious  of  the  value  of  the  plumes,  may  it  not  be  asked  why  the  female  is 
unable  to  'see  what  plumes  are  most  effective?'  The  mental  state  in  the  male 
is  without  meaning  unless  we  suppose  the  female  to  be  affected  and  pleased." 
(Peckham,  loc.  cit.,  p.  144.) 

In  regard  to  another  interpretation  of  the  courtship,  the  Peckhams 
point  out: 

"Mr.  Pocock  has  suggested  that  the  attitude  of  observant  interest  on  the 
part  of  the  female  spider  might  be  taken  to  indicate  that  she  was  preparing  to 
spring  upon  her  mate  and  devour  him;  or  that  it  might  simply  mean  that  she 
was  warily  guarding  herself  from  his  approach.  Neither  of  these  suppositions 
is  admissible.  In  some  species  the  male  is  not  attacked  by  the  female,  and 
when  she  does  wish,  as  frequently  happens,  either  to  avoid  or  to  destroy  him, 
her  attitude  is  totally  different.  In  the  former  case  she  turns  about  and  runs 
rapidly  away,  or  suspends  herself  by  a  thread  of  web.  In  the  second,  there  is  a 
contraction  of  all  the  muscles,  the  legs  are  drawn  together,  and  in  this  crouch- 
ing position  she  creeps  slowly  toward  him,  as  she  might  if  he  were  a  fly,  only 
with  something  more  malignant  in  her  aspect.  When  she  takes  this  stand  the 
male  incontinently  flees.  When,  on  the  contrary,  the  female  is  interested  in 
the  male  display,  she  seems  perfectly  absorbed  in  watching  him,  the  muscles 
are  all  relaxed,  unconscious  of  herself  she  directs  her  glance  now  here,  now 
there,  as  he  moves  about;  as  he  continues  his  mad  antics,  her  appearance  gives 
every  indication  of  pleasurable  excitement,  and  as  he  comes  closer  and  closer, 
she  yields  herself  to  the  impulses  which  he  has  awakened  in  her,  and,  as  in 
pulex,  joins  in  his  dance  and  whirls  around  and  around  as  though  intoxicated. 
We  claim,  then,  to  have  completely  answered  Mr.  Wallace's  first  objection." 
(Peckham,  loc.  cit.,  pp.  145,  146.) 

Finally,  in  regard  to  the  specific  character  of  the  display  of  the 
males,  the  Peckhams  make  the  following  significant  statement: 

1  Among  the  most  remarkable  of  this  wonderful  family  are  the  nine  species  of  coquettes  (Loph- 
ornis),  which  have  elongated  feathers,  with  metallic  tips,  springing  from  the  sides  of  the  neck; 
some  have  also  beautiful  crests.  (George  W.  and  Elizabeth  G.  Peckham.,  Additional  Observa- 
tions on  Sexual  Selection  in  Spiders  of  the  Family  Attidae.,  Nat.  Hist.  Soc.  of  Wisconsin,  1889, 
vol.  I,  pp.  141,  142.) 

2  Tropical  Nature,  p.  210.     The  italics  are  ours. 


RELATING   TO    SECONDARY    SEXUAL    CHARACTERS.  59 

"The  spider  has  four  pairs  of  legs,  and  all  are  equally  available  for  display 
or  locomotion,  and  since  all  the  movements  are  slow  and  on  the  ground  they 
are  entirely  open  to  observation  and  study,  and  we  arc  thus  in  a  portion  to 
decide  by  facts  whether  their  activity  is  simply  an  outlet  for  superfluous 
energy,  and  therefore  meaningless,  or  whether  there  is  a  purpose  in  it.  If  the 
purpose  of  the  antics  is  only  to  let  off  energy,  then  wo  should  expect  one-  pail 
to  be  flourished  around  quite  as  often  as  another,  and  that  the  pair  flourished 
should  as  frequently  be  one  that  was  not  ornamented  as  one  that  was;  and, 
moreover,  their  movements  ought  not  to  be  of  such  a  nature  as  to  display  the 
color  or  ornament  more  frequently  than  the  law  of  chance  would  explain.  If 
the  spider  almost  always  moves  the  ornamented  legs,  and  in  such  a  way,  too, 
as  to  bring  out  their  beauty,  it  would  seem  to  us,  to  say  the  least,  highly 
improbable  that  the  dance  of  the  spider  was  merely  a  meaningless  overflow  of 
surplus  energy.  Such  an  explanation  leaves  much  that  needs  explanation. 
The  facts  are,  that  the  best  foot  is  put  forward;  and  this  is  just  what  Darwin's 
theory  requires  and  explains.  Under  Mr.  Wallace's  view  the  facts  are  inex- 
plicable. The  better  to  show  that  these  movements  are  not  simply  meaning- 
less outlets  of  high  vigor,  we  illustrate  the  several  positions  by  figures  taken 
from  nature  (figs.  7-12).  The  figures  would  seem  to  prove  that  the  legs  that 
are  ornamented  or  contrasted  in  color  are  also  the  legs  that  are  usually  flour- 
ished; that  where  none  of  the  legs  have  special  ornament,  then  all  are  used;  or, 
as  sometimes  happens,  when  an  unornamented  leg  is  used  the  movements  are 
of  such  a  character  as  to  display  some  ornament  that  would  otherwise  have 
been  more  or  less  hidden  from  the  female."     (Peckham,  loc.  cit.,  p.  147.) 

In  the  tarantula,  Petrunkewitsch  finds  that  sight  plays  no  role  in 
mating — that  it  is  due  entirely  to  accidental  contact  between  the  male 
and  female.  Here  the  sexes  are  closely  alike,  except  for  a  pair  of  hooks 
on  the  front  legs  of  the  male,  by  means  of  which  he  grasps  the  mandibles 
of  the  female,  holding  them  during  the  elaborate  process  of  trans- 
ference to  her  genital  opening  the  sperm  that  he  has  already  collected 
in  the  genital  spoon  on  his  palpi.  The  hooks  serve  to  guard  the 
male  against  injury  or  death,  wrhile  at  the  same  time  they  aid  him  in 
the  act  of  coitus. 

In  a  common  spider,  Mceiia  villata,  two  kinds  of  males  exist.  Both 
have  been  seen  to  mate  with  the  same  female.  No  preference  is  given 
to  either  type.  The  difference  between  them,  according  to  Painter, 
is  connected  with  or  caused  by  an  additional  pair  of  chromosomes  in 
the  gray  male.  The  two  types  may  therefore  have  no  connection  with 
sexual  selection,  but  be  directly  due  to  a  difference  in  the  chromosome 
group. 

Montgomery,  who  made  observations  on  the  courting  habits  of 
several  species  of  spiders,  states  that  his  ''general  theoretical  con- 
clusions were  quite  different  from  those  of  the  Peckhams."  It  turns 
out,  however,  that  his  objection  to  their  view  is  based  entirely  on  their 
assumption  that  the  male  is  conscious  of  his  display  and  that  the 
female  is  guided  by  an  esthetic  sense  in  selecting  the  more  beautiful 
male.    It  should  be  pointed  out  that  even  after  the  removal  of  tl 


60  THE    GENETIC    AND    THE    OPERATIVE    EVIDENCE 

gratuitous  assumptions  as  to  the  cause  of  the  evolution  of  the  male 
and  female,  enough  still  remains  in  Montgomery's  own  observations 
to  include  his  results  on  courtship  under  Darwin's  theory  of  sexual 
selection.    For  example,  Montgomery  says: 

"The  adult  male  is  excited  simultaneously  by  fear  of  and  desire  for  the 
female,  and  his  courtship  motions  are  for  the  most  part  exaggerations  of  ordi- 
nary motions  of  fear  and  timidity.  By  such  motions  he  advertises  himself  to 
the  female  as  a  male,  but  there  is  no  proof  that  he  consciously  seeks  to  arouse 
her  eagerness  by  esthetic  display — there  seems  to  be  no  good  reason  to  hold 

that  the  female  is  actuated  in  her  choice  by  sensations  of  beauty 

Thus  my  opinion  was  opposed  to  Darwin's  theory." 

Now,  it  is  obvious  that  if  a  more  brightly  colored  male  has  a  better 
chance  of  " advertising  himself"  to  the  female  all  the  essential  require- 
ments of  Darwin's  theory  are  fulfilled,  regardless  of  whether  the  male 
is  conscious  of  his  ornamentation  or  the  female  makes  use  of  an  "  esthe- 
tic sense."  In  another  passage  (p.  173)  Montgomery  concedes  all 
that  any  modern  critical  advocate  of  Darwin's  theory  is  likely  to  ask: 

"We  have  previously  seen  that  conscious  aesthetic  choice  by  the  female 
probably  does  not  account  for  such  male  characters  [secondary  sexual  charac- 
ters with  their  'conspicuous  color  markings'];  that  they  are  accordingly, 
probably  not  due  to  sexual  selection.  These  characters  of  the  males  may  be 
most  readily  explained  as  being  conceived  by  simple  natural  selection.  Pecu- 
liar ornamentation  would  be  selected  because  unusually  greater  sex  recogni- 
tion therefore  prompted  mating." 

It  is  evident  that  Montgomery  has  only  shifted  the  situation,  although 
to  advantage,  I  think,  but  is  essentially  in  accord  with  Darwin's  theory 
of  sexual  selection,  despite  his  protest  to  the  contrary.  The  difference 
lies  in  Darwin's  and  especially  in  the  Peckhams'  use  of  the  term 
" choice,"  "aesthetic  sense,"  etc.,  to  stand  for  the  fact  that  the  female 
more  promptly  mates  (as  Montgomery  prefers  to  put  it)  with  a  male 
peculiarly  ornamental. 

The  most  critical  observations  on  sexual  selection  that  have  been 
made  in  the  group  of  insects  are  those  by  Sturtevant  on  the  pomace 
fly.    The  courtship  is  described  as  follows : 

"The  first  and  most  noticeable  act  in  courtship  occurs  when  the  male,  being 
near  the  female,  extends  one  wing  at  about  right  angles  to  his  body,  and 
vibrates  it  for  a  few  seconds.  The  wing  is  then  returned  to  the  normal  position 
and  the  process  is  repeated,  usually  with  the  other  wing.  But  between  times 
there  is  a  scissors-like  movement  of  the  wings  repeated  several  times.  This 
vibrating  of  the  wings  is  often  repeated  many  times,  and  may  be  done  in  any 
position  relative  to  the  female,  though  the  male  always  faces  her.  Usually, 
in  fact,  he  swings  quickly  around  her  in  a  semicircle  once,  or  oftener,  during 
the  process.  Soon  the  male  begins  to  protrude  his  genitalia  and,  if  the  female 
remains  quiet,  to  lick  her  posterior  end.  Some  white  matter  now  protrudes 
from  her  ovipositor,  and  other  males  in  the  same  vial  are  usually  observed  to 
become  excited  now  and  begin  courting,  indicating  odor  as  a  cause  of  sexual 
excitement.     If  the  female  runs  or  flies  away  the  male  is  excited,  moves  his 


RELATING    TO    SECONDARY    SEXUAL    CHARACTERS.  61 

wings  jerkily,  and  walks  around  rapidly,  but  seems  unable  to  follow  the  female 
accurately  or  to  locate  her  quickly.  The  penis  is  directed  forward  l>y  bending 
up  the  abdomen  underneath,  towards  the  thorax,  and  is  jerked  toward  the 
female  (the  male  always  standing  facing  her  at  this  stage),  but  not  always 
toward  her  genitalia,  as  I  have  seen  it  strike  her  in  the  eye.  (The  male  in 
this  case,  however,  had  white  eyes,  and  so  was  perhaps  blind.  Normally  the 
aim  is  accurate.)  If  it  does  strike  the  mark  the  male  mounts  on  the  female's 
back,  between  her  wings.  Mounting  never  takes  place  until  after  the  actual 
copulation  has  occurred,  in  which  respect  Drosnphila  differs  from  some  related 
flies  (e.  g.,  Muscidse,  Anthomyidae,  Sepsidaj,  Borboridae,  and  Ephydridse,  so  far 
as  my  observations  go).  In  these  forms  the  male  flies  and  lights  on  the  female, 
after  which  copulation  may  or  may  not  take  place,  probably  depending  upon 
the  way  the  female  responds."  ! 

To  test  whether  the  wings  have  any  significance  in  courtship,  the 
wings  of  a  male  were  clipped  off  and  he  was  put  into  competition  with 
a  normal  male  of  the  same  stock,  age,  and  size.     A  virgin  female 
sexually  mature  was  given  to  these  two  males.     The  normal  male 
mated  72  times  before  the  other,  the  clipped  male  53  times.    It  might 
appear  that  the  female  selected  the  normal  male  in  preference  to  the 
clipped  one,  or  possibly  that  the  male  with  normal  wings  drove  the 
other  male  away.     That  the  operation  on  the  wings  may  have  an 
influence  on  the  male  himself  is  shown  in  McEwen's  results.    He  found 
that  clipped  males  lost  their  heliotropism.    It  was  also  possible  that 
the  courtship  of  the  normal  male  might  make  the  female  ready  to 
copulate  and  then  she  would  mate  with  either  male.     Sturtevant 
tested  the  last  supposition  by  placing  single  pairs  in  vials,  testing  each 
day  an  equal  number  of  normal  and  clipped  males.     The  length  of 
time  before  copulation  was  noted.    The  clipped  male  began  to  court 
as  soon  as  the  normal,  but  a  larger  number  of  normal  males  mated  in 
the  first  12  minutes  than  clipped  males  (59  to  25).    Had  the  females 
discriminated  against  the  clipped  males  to  an  equal  extent  we  would 
have  expected  a  much  greater  excess  than  72  to  53  when  they  were  in 
competition.    It  appears,  then,  that  the  wings  are  useful  in  shortening 
the  time  between  the  meeting  of  the  individuals  and  copulation.    The 
display  acts,  however,  almost  as  favorably  for  the  other  male  as  for 
the  exhibitor  himself.    The  results  showr,  therefore,  that  here  an  est  hetic 
sense  of  the  female  need  not  be  postulated,  for  she  actually  shows  little 
preference  when  she  has  been  brought  to  the  point  of  mating  between 
the  male  that  aroused  her  and  the  other  male  that  did  not.     This 
critical  test  puts  the  problem  in  a  different  relation  from  that  which 
Darwin's  theory  of  female  choice  was  meant  to  throw  light  upon. 

The  reverse  experiment — a  clipped  and  a  normal  female  of  the  same 
age,  size,  etc. — showed  that  the  male  did  not  discriminate  between 
them,  for  in  52  first  trials  the  normal  female  was  paired  with  25  tunes, 
the  clipped  27  times. 

'A.  H.  Sturtevant.     Experiments  on  Sex  Recognition  and  (he  Problem  of  Santa!  Bateetta  in 
Drosophila.     Journ.  Animal  Behavior,  Sept.-Oct.  1915,  vol.  5,  No.  5,  pp.  352,  353. 


62  THE    GENETIC   AND   THE    OPERATIVE   EVIDENCE 

PART  III. 
THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE. 

The  genetic  and  operative  evidence  shows  that  there  has  been 
included  under  the  general  term  "secondary  sexual  characters"  a 
complex  of  cases  that  are  the  outcome  of  diverse  physiological  processes. 
Sex-linked  and  sex-limited  characters  have  often  been  confused;  some 
characters  depend  on  the  gonad;  some  of  these  involve  the  ovary, 
others  the  testes.  Still  other  characters  fall  under  none  of  these  groups, 
but  are  the  direct  product  of  the  male  or  female  genetic  constitution. 
It  is  not  surprising,  therefore,  that  theories  proposed  on  the  informa- 
tion derived  from  certain  of  these  data  are  controverted  by  information 
derived  from  other  data.  The  theory  of  sexual  selection,  in  its  attempt 
to  bring  all  the  facts  under  one  point  of  view,  has  not  escaped  these 
difficulties,  even  although  it  may  be  said  that  neither  natural  selection 
nor  sexual  selection  is  concerned  with  the  origin  or  even  the  kind  of 
variations  with  which  it  works.  Nevertheless,  the  latter  theory,  by 
ignoring  the  origin  or  the  physiological  process  concerned  in  the 
production  of  secondary  sexual  characters,  may  make  assumptions 
that  are  difficult  to  harmonize  with  the  facts  in  the  case,  and  we  shall 
find  several  instances  of  this  sort.  For  example,  if  the  hen  had  selected 
the  cock  for  his  fine  plumage  (which,  as  we  have  seen,  depends  in  part 
on  autosomal  genes  producing  their  effect  without  the  cooperation  of 
the  testes),  she  would  be  expected  to  endow  herself  with  the  same 
adornments  (if  her  selection  worked),  unless  her  ovary  were  already 
producing  some  substance  inimical  to  those  that  she  is  " calling  forth" 
by  selection  of  the  male.  The  problem  is  evidently,  then,  more  com- 
plex than  appears  on  the  surface,  and  is  not  so  simple  as  it  seemed 
when  these  essential  facts  were  unknown  or  ignored. 

In  the  case  of  other  theories,  such  as  those  of  Wallace  and  of  Cun- 
ningham (that  appeal  more  directly  to  the  causes  that  are  producing 
the  variation  out  of  which  the  secondary  sexual  characters  are  built 
up),  the  absence  of  information,  physiological  or  genetic,  has  only  too 
often  given  these  writers  the  opportunity  to  speculate  without  the  re- 
straints which  a  more  recent  knowledge  of  the  facts  has  imposed  on  us. 

It  is  obvious  from  what  we  have  learned  that  we  shall  have  to  proceed 
with  more  caution  in  disentangling  the  evidence  before  we  can  hope  to 
" explain"  it.  Despite  the  meagerness  of  our  present  information, 
enough  has  been  found  out  to  indicate  that  we  must  be  content  for 
a  while  with  tentative  and  partial  explanations  even  in  the  best- 
known  cases,  and  we  must,  I  think,  be  prepared  to  admit  that  no  one 
theory  may  be  able  to  account  for  all  of  the  secondary  sexual  differences 
that  exist  between  the  sexes. 

The  genetic  evidence  shows,  in  the  case  of  cock-feathering  versus 
hen-feathering  in  birds,  that  only  one  or  two  Mendelian  factor  differ- 


RELATING    TO    SECONDARY    SEXUAL    CHARACTERS.  G3 

ences  are  involved.  The  result  may  seem  to  mean  that  the  secondary 
sexual  characters  themselves  have  been  acquired  historically  by  a  single 
evolutionary  step,  and  that  in  consequence  the  opportunity  for  selec- 
tion to  have  accomplished  such  a  result  has  been  enormously  facilitated. 
Such  an  argument  rests,  however,  as  we  know  to-day,  on  a  false  inter- 
pretation of  Mendelian  heredity.  What  the  evidence  really  shows  is 
that  one  or  two  genes  if  present  cause  the  testes  to  produce  some 
substance  that  prevents  the  cock-feathering  from  developing.  The 
genetic  complex  may  require  a  hundred  or  a  thousand  or  more  special 
factors  that  are  directly  and  indirectly  concerned  with  the  development 
of  the  cock-feathering,  but  one  or  two  other  factors  may  suffice  to  block 
this  machinery;  or,  to  change  the  metaphor,  these  dominant  factors 
may  be  no  more  than  so  much  sand  poured  into  the  clock.  The  clock 
may  have  been  slowly  built  up  historically  by  many  contributory 
"factors,"  but  a  little  sand  may  spoil  its  activity.  Similarly  in  the  hen 
something  produced  by  the  ovary  prevents  the  fullest  possible  genetic 
action  from  taking  place.  Here  at  present  we  do  not  know  whether  a 
single  factor  or  a  hundred  "special"  factors  are  necessary  to  produce 
such  an  inhibition,  but  if,  as  one  would  like  to  suppose,  it  is  the  same  or 
partly  the  same  genes  involved  in  the  ovary,  and  in  the  testes  of  hen- 
feathered  males,  then  a  relatively  few,  one  or  two,  factors  will  suffice 
to  bar  cock-feathering  from  the  female. 

In  a  case  like  the  clover  butterfly,  where  the  genetic  relations  work 
out  on  the  theory  of  one  pair  of  factors  that  produce  two  types  of 
females  and  one  type  of  male,  it  seems  more  reasonable  to  infer  that 
such  a  difference  has  not  been  slowly  acquired  by  many  smaller  muta- 
tional changes,  because  the  two  types  are  not  adapted  to  live  under 
two  different  environments  for  which  their  differences  fit  them  respec- 
tively, but  to  live  in  the  same  environment.  It  has  never  been  claimed, 
so  far  as  I  know,  that  these  two  types  of  females  have  arisen  through 
some  males  preferring  one,  some  another  kind  of  female,  so  that  even 
although  it  may  seem  probable  that  the  genetic  situation  is  simple, 
the  simplicity  can  not  be  turned  to  the  advantage  of  the  theory  of 
sexual  selection.  It  is  unnecessary  to  discuss  further  the  origin  of  the 
factor  or  factors  suppressing  the  development  of  one  type  in  the  male 
or  the  probability  of  the  multiplicity  of  such  factors.  In  the  rase  (if 
such  species  as  Papilio  memnon  and  P.  polytes,  with  three  types  <>t 
females,  the  situation  is  the  same  as  above,  with  the  addition  of  the 
theory  of  mimicry,  that  "explains"  some  advantage  accruing  t.»  each 
type  of  female.  Since  the  latter  is  only  a  form  of  natural  selection, 
we  are  not  further  concerned  with  the  change  here.  Punnet  t  's  excellent 
treatment  of  the  problems  involved  in  his  recent  book  on  mimicry 
brings  the  subject  down  to  date. 

Meager  as  is  the  genetic  and  surgical  evidence  at  present,  it  is  enough 
to  show  that  only  by  further  work  along  these  lines  can  we  hope  to  lay 


64  THE   GENETIC   AND   THE    OPERATIVE   EVIDENCE 

a  firm  foundation  for  a  scientific  study  of  the  subject.  It  is  equally 
important  that  critical  evidence  be  obtained  in  regard  to  the  effect  on 
the  female  of  males  of  different  types  in  competition.  The  instinctive 
reactions  of  animals  in  these  respects,  their  first  reaction,  the  asso- 
ciations that  may  or  may  not  result,  are  practically  an  open  field  for 
investigation.  The  entire  equipment  of  human  psychology  of  the  in- 
trospective school,  that  has  been  appealed  to  for  help  in  a  situation 
itself  little  understood,  reads  often  more  like  fiction  than  like  science. 

So  far  as  one  branch  of  the  subject  goes — the  possible  interpretation 
of  ornamentation  in  the  male — there  seem  to  be  two  ways  at  least  in 
which  the  subject  calls  for  immediate  investigation:  First,  if  it  can  be 
shown  that,  other  things  being  equal,  a  more  adorned  male  rouses  the 
female  to  prompter  mating,  it  may  be  inferred  with  some  probability 
that  in  the  long  run  such  conduct  would  lead  to  the  establishment  of 
the  more  effective  individual,  but  this  would  not  be  true  unless  the 
males  mate,  as  a  rule,  more  than  once,  for  any  advantage  that  might 
accrue  to  a  more  ornamented  male  would  not  affect  the  course  of  evolu- 
tion of  the  species  if  every  other  male  found  a  mate  too.  Second,  if  it 
could  be  shown  that  the  special  ornamentation  of  the  male  is  only  one 
of  several  effects  of  a  gene  whose  main  effect  is  in  some  other  direction, 
then  the  advantage  gained  through  natural  selection  in  this  other 
direction  would  carry  in  its  wake  the  advance  in  ornamentation,  and  if 
the  change  affects  one  sex  more  than  the  other,  owing  to  the  difference 
in  the  genetic  complex  of  the  two  sexes,  it  would  be  called  a  secondary 
sexual  character. 

A.  Evidence  from  Mammals. 

Owing  to  the  differences  in  the  secondary  sexual  characters  of  dif- 
ferent breeds  of  sheep,  we  have  more  genetic  information  about  such 
characters  in  this  group  than  in  other  groups  of  mammals.  For- 
tunately, also,  in  some  of  the  breeds  both  castration  and  ovariotomy 
have  been  performed,  and  consequencely  we  are  in  position  to  utilize 
both  sources  of  information  for  interpreting  the  situation.  In  certain 
breeds  both  males  and  females  have  horns  (Dorsets),  in  which  case  the 
horns  of  the  male  are  larger  than  those  of  the  female.  In  other  breeds 
neither  males  nor  females  have  horns  (Suffolks).  In  still  other  breeds 
the  males  have  horns  and  the  females  are  hornless  (Merinos  and  Herd- 
wicks).  The  clearest  evidence  that  we  have,  both  genetic  and  opera- 
tive, is  that  obtained  by  Woods,  as  reported  by  Bateson,  in  which 
horned  (Dorsets)  and  hornless  (Suffolks)  breeds  were  crossed.  In  the 
Dorsets,  where  both  sexes  have  horns,  those  of  the  male  are  larger  than 
those  in  the  female.  When  the  young  male  is  castrated  the  horns 
develop,  but  only  as  far  as  in  the  female.  It  appears,  therefore,  that 
the  presence  of  the  testis,  probably  through  some  secretion  from  it, 


RELATING   TO    SECONDARY    SEXUAL    CHARACTERS.  65 

contributes  to  the  development  of  the  horns.  The  other  race,  the 
Suffolks,  have  no  horns  in  either  sex.  Castration  produces  no  change 
in  their  hornless  condition. 

When  a  Dorset  ram  is  crossed  to  a  Suffolk  ewe  the  sons  have  horns, 
the  daughters  lack  them.  The  reciprocal  cross  gives  the  same  results. 
The  factor  or  factors  involved  are  therefore  not  sex-linked.  When 
the  Fi's  from  the  cross  or  from  its  reciprocal  are  inbred,  four  classes 
of  offspring  are  produced,  namely:  Horned  male,  3;  hornless  male,  1 ; 
horned  female,  1 ;  hornless  female,  3.  The  ratios,  as  above,  are  approxi- 
mately 3:1:1:3. 

A  simple  Mendelian  explanation  covers  the  results.  If  we  assume 
that  the  Dorsets,  both  male  and  female,  are  homozygous  in  a  factor 
for  horns,  H,  that  is  not  in  the  sex  chromosome,  and  that  the  Suffolks 
"lack  this  factor,"  i.  e.,  that  they  have  an  allelemorphic  factor  for 
hornlessness,  the  germ-cells  are  H-H  and  h-h,  respectively.  Only 
one  kind  of  individual,  Hh,  results  in  Fi.  Since  the  male  with  this 
formula  develops  horns,  we  must  conclude  that  the  presence  of  the 
testis  (through  its  secretions)  causes  horns  to  develop,  while  in  the 
female  of  this  same  composition  horns  are  not  produced  because  of  the 
absence  of  the  testes.  The  sex-cells  in  these  Fi  individuals  are  H-h 
and  H-h.  Chance  meeting  of  these  gametes  will  give  3  classes  of 
individuals,  irrespective  of  sex,  namely,  (1)  HH,  (2)  Hh,  (1)  hh.  The 
expectation  for  the  males  is  that  those  of  the  composition  (1)  HH  and 
(2)  Hh  will  develop  horns,  while  those  of  the  composition  hh  will  not 
develop  horns.  There  should  be  3  horned  to  1  hornless  male.  In  the 
females  we  expect  those  with  the  composition  (1)  HH  to  develop 
horns,  since  they  have  the  same  formula  as  the  pure  Dorset ;  those  with 
the  formula  Hh  are  not  expected  to  develop  horns,  because  the  Fi  females 
of  this  composition  do  not  have  horns;  those  with  the  formula  hh  are 
not  expected  to  develop  horns,  because  they  have  the  same  composit  Loo 
as  have  the  pure  Suffolk.  There  should  be  3  hornless  to  1  horned 
female.  Combining  both  sexes,  the  expectation  for  F2  is  4  horned  to 
4  hornless.  Arranged  according  to  sex,  these  give  the  classes  realized. 
Horned  male,  3;  hornless  male,  1 ;  horned  female,  1 ;  hornless  female,  3. 
That  this  is  the  correct  explanation  is  borne  out  by  back-crossing  the 
hornless  Fi  female  to  a  hornless  Suffolk  ram.  The  former  has  two 
kinds  of  gametes,  H  and  h,  the  latter  only  gametes  that  bear  the  h 
factor.  Half  the  sons  should  be  horned,  half  hornless,  because  half  of 
them  are  Hh  and  half  hh.  But  none  of  the  daughters  should  have 
horns,  because  neither  the  Hh  nor  the  hh  females  produce  horns.  This 
is  the  result  realized,  viz,  3  hornless  offspring  to  1  horned. 

The  preceding  account  of  the  inheritance  of  the  factor  for  horns  is 
based  on  the  combination  of  Dorsets  and  Suffolks  used  by  Wood. 
That  other  conditions  may  exist  in  other  breeds  and  even  in  races  of 


66       THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

the  same  breed  is  claimed  by  Arkell  as  a  result  of  a  large  number  of 
crosses  that  he  has  carried  out.  He  states,  for  instance,  that  in  the 
great  Merino  class,  with  its  various  sub-breeds,  there  are  flocks  in 
which  the  males  only  are  horned,  but  even  here  there  may  be  individual 
males  that  are  hornless  "and  at  times  the  females  may  also  show  some 
signs  of  horn  growth."  In  America,  Arkell  states,  there  are  three 
types  of  Merinos — the  American,  the  Delaine,  and  the  Rambouillet. 
He  quotes  Plumb  (Types  and  Breeds  of  Farm  Animals,  Boston,  1906) 
as  stating  that  "the  American  Merino  ram  carries  heavy,  spirally 
twisted  horns,  but  the  ewes  are  hornless ;  .  .  .  .  that  the  rams  of  the 
National  Standard  or  Victor-Beald  Delaines  may  or  may  not  have 
horns ;  that  the  Dickinson  Delaines  may  have  small  horns,  but  a  polled 
head  is  pref erred,' '  etc.  These  conditions  suggest  that  there  may  be 
more  than  a  single  factor  for  horns  in  sheep  or  that  there  may  be 
modifying  factors  in  certain  breeds.  In  fact,  Arkell  and  Davenport 
attempt  to  cover  the  results  of  Arkell's  experiments  by  assuming  that 
there  is  an  inhibiting  factor  for  horns  that  is  carried  by  the  sex  chromo- 
some. Such  an  inhibitor  (I)  would  be  double  in  the  XX  female  and 
single  in  the  X  male.  It  is  assumed  to  be  incapable  of  preventing  the 
development  of  horns  in  the  heterozygous  Hh  male,  the  inhibitor  being 
there  simplex  (i.e.,  one  I),  while  the  double  inhibitor  is  capable  of  prevent- 
ing the  horns  in  the  heterozygous  (Hh)  condition,  but  not  of  preventing 
the  development  of  horns  when  the  homozygous  (HH)  condition 
occurs.  There  are  several  objections  to  this  scheme:  first,  that  there  is 
no  evidence  that  a  sex-linked  inhibitor  is  present  that  affects  the  horn- 
less breeds,  for  the  evidence  indicates  rather  that  there  is  no  factor  for 
horns  present  in  them,  at  least  in  the  Suffolks;  second,  the  peculiar 
balance  between  the  factors  for  horns  and  the  inhibitor  seems  an 
extremely  artificial  statement.  Arkell  and  Davenport  intimate  that 
races  with  horned  males  and  hornless  females  do  not  exist  in  a  pure 
state.  That  breeds  impure  in  these  respects  may  exist  need  not  be 
denied,  but  that  pure  races  for  such  a  dimorphic  condition  do  exist 
seems  probable.  Castle  states,  for  instance,  that  he  knows  at  first 
hand  of  such  races  of  Merinos.  Castle  also  states  that  castrated  Merino 
rams  in  this  race  do  not  develop  horns,  and  this  result  is  in  accordance 
with  statements  made  by  Marshall  for  Herdwicks  (a  race  with  horned 
males  and  hornless  females).  Under  the  circumstances  it  is  certain 
that  the  presence  of  the  testes  is  one  of  the  factors  in  determining 
whether  horns  develop  at  all  (as  in  Merinos),  or  in  determining  the 
extent  to  which  they  develop  (as  in  the  Dorsets),  rather  than  that  the 
difference  between  the  sexes  is  due  only  to  an  inhibiting  genetic  factor. 
Nevertheless,  it  may  be  well  to  keep  open  the  possibility  that  there  may 
be  different  factors  for  horns  in  different  races  (allelomorphs  or  others), 
or  conversely,  that  the  genetic  composition  of  the  races  is  different,  the 
factor  for  horns  remaining  the  same,  but  producing  a  different  effect. 


RELATING   TO    SECONDARY    SEXUAL    CHARACTERS.  67 

It  may  be  pointed  out  in  passing  that  if,  as  Arkell  assumes,  the 
hornless  races  are  due  to  the  presence  in  them  of  an  inhibitor  for  horns, 
the  results  can  be  worked  out  without  postulating  that  the  inhibitor 
is  sex-linked.  For  example,  if  the  hornless  male  and  female  be  H II 1 1 
and  the  horned  male  and  female  HHii,  the  F!  horned  males  and 
hornless  females  will  be  HHIi.  The  germ-cells  will  be  HI  and  Hi  in 
each  sex,  which,  by  chance  meeting,  as  shown  below,  gives  the  results 
obtained  by  Wood.    Thus: 

HI  v/  Hi female. 

HIAHi male. 


1H1HI+2,  HIHi+1,  HiHi. 

These  formula?  give  3  horned  males,  1  hornless  male,  1  horned 
female,  3  hornless  females.  This  formulation,  while  appealing  appar- 
ently to  a  different  set  of  factors  from  those  used  by  Arkell,  is  in  reality 
the  same  in  principle,  since  the  heterozygous  condition  is  here  repre- 
sented by  Ii  (instead  of  Hh)  and  sex  determines  that  the  heterozygous 
male  is  horned  and  the  female  hornless. 

The  genetic  relations  of  the  Merino  with  horned  males  and  hornless 
females  to  the  Dorsets,  in  which  both  sexes  are  horned  (but  in  the 
male  the  horns  are  larger),  must  be  different  from  the  genetic  relation 
in  the  other  cross.  There  are  two  theoretical  possibilities,  viz,  that  a 
different  factor  for  horns  is  present  that  is  either  an  allelomorph  or 
another  different  factor;  or  second,  that  a  modifier  is  present  in  the 
Merino  that  keeps  down  the  development  of  the  horns  in  the  female. 
An  answer  could  be  obtained  by  breeding  Merinos  to  horned  and  to 
hornless  and  getting  F2  from  both  crosses.  Arkell's  data  is  not  sufficient 
to  settle  the  question,  because  his  numbers  are  often  too  small,  but 
chiefly  because  it  appears  that  there  were  two  genetic  types  present 
in  his  flock  of  Merinos,  one  of  which  is  characterized  by  scurs  (very 
short  horns)  in  the  females,  the  other  by  hornlessness  in  the  female. 
He  found  in  a  cross  between  a  hornless  father  and  Merino  mother 
(that  had  knobs  or  scab-like  growths)  that  the  daughters  had  horns 
or  scurs  and  carried  a  determiner  for  horns  (as  subsequent  generations 
showed).  On  the  other  hand,  in  other  cases  where  the  Merino  mother 
was  without  horns,  her  Fi  daughters  had  no  horns.  In  both  easts  the 
Fi  sons  had  horns.  Arkell  cites  this  cross  as  "proving"  that  the  knobs 
of  Merino  ewes  depend  for  their  development  upon  two  horn  deter- 
miners (H'H').  It  is  not  at  all  evident  that  the  results  lead  to  such 
a  conclusion,  as  other  explanations  will  cover  the  ease  as  well. 

Arkell's  mating  between  Dorsets  and  Merinos  (tables  EX  and  \vi) 
corroborates  his  view  "that  the  knob  of  the  Merino  female  is  repre- 
sented in  the  germ-plasm  by  the  double  determiner."  The  5  I\  bods 
had  long  horns,  3  Fi  daughters  had  horns  present,  and  2  had  them 
absent  (table  xvi).  If  some  of  the  Merino  mothers  used  were  homo- 
zygous for  a  factor  that  inhibits  the  development  of  horns  in  the  female 


68  THE    GENETIC    AND    THE    OPERATIVE    EVIDENCE 

we  can  account  for  the  hornless  daughters,  and  if  other  mothers  did 
not  have  this  factor  (or  were  heterozygous  for  it)  we  can  account  for 
the  horned  daughters.  Evidently  more  evidence  is  needed.  Arkell 
himself  assigns  a  corresponding  difference  to  the  mothers  in  these  cases, 
based  on  the  observed  fact  that  the  mother  that  had  knobs  or  scurs 
were  the  ones  that  gave  birth  to  the  horned  daughters.  If  the  above 
suggestion  proves  true,  it  shows  that  the  Merino  condition  dominates 
the  Dorset  condition.  The  result  is  in  harmony  with  the  view  that 
both  have  a  common  factor  for  horns,  but  that  in  addition  the  Merinos 
have  a  non-sex-linked  modifier  that  holds  down  the  development  of  the 
horns  in  the  ewe. 

What  bearing  have  these  results  on  the  theory  of  sexual  selection? 
Clearly  the  Merino  male,  as  constituted  at  present,  develops  horns 
because  he  is  a  male,  but  only  in  the  sense  that  his  testes  secrete  some 
substance  that  makes  his  horns  grow.  That  maleness  does  not  in  itself 
necessarily  produce  horn  is  shown  by  the  absence  of  horns  in  the 
Suffolk  breed.  Is  it  the  same  factor,  present  in  the  Merino,  that 
produces  horns  in  both  sexes  of  Dorsets  when  homozygous  and  in  the 
male  only  when  heterozygous?  If  originally  the  ancestral  race  had  no 
horns,  the  appearance  of  factors  for  horns  would,  even  in  a  heterozygous 
condition,  have  sufficed  in  the  males  for  the  development  of  horns. 
If  this  gave  them  any  advantage  either  over  the  enemies  of  the  race  or 
in  the  eyes  of  the  female,  such  factors  might  be  perpetuated,  and 
through  transferrence  to  the  females  ultimately  become  homozygous 
in  both  sexes.  Both  would  then  have  horns,  whether  horns  were  or 
were  not  of  any  advantage  to  the  female,  which  would  have  them 
because  they  have  an  advantage  to  the  other  sex. 

Because  the  genetic  evidence  shows  that  a  single  factor  difference 
between  the  breeds  with  and  without  horns  accounts  for  the  horned 
condition  in  one  of  them,  it  by  no  means  follows  that  horns  as  they 
exist  arose  as  a  single  mutant  factor  change.  True,  they  may  have 
arisen  as  a  new  single  factor  difference,  but  the  Mendelian  evidence 
can  not  be  claimed  as  evidence  for  this  view.  The  a  priori  argument 
based  on  the  relation  of  horns  in  an  adaptive  sense  to  the  rest  of  the 
body  would  appear  rather  to  indicate  that  they  could  not  have  arisen 
at  a  single  mutational  step. 

Concerning  the  still  broader  bearing  of  this  evidence  on  the  theory 
of  sexual  selection,  two  distinct  questions  are  involved:  first,  how  has 
the  present  racial  difference  in  horns  arisen  in  domesticated  sheep,  and 
secondly,  what  was  the  original  condition  of  sheep.  Reversing  the 
order  of  these  questions,  we  find  that  sheep  were  domesticated  in  Asia 
and  Europe  before  the  dawn  of  history.  "Whether  our  well-known 
and  useful  animal  is  derived  from  any  one  of  the  existing  wild  species, 
or  from  the  crossing  of  several,  or  from  some  now  extinct  species,  is 
quite  a  matter  of  conjecture"  (Flower  and  Lydekker's  "Mammals"). 


RELATING   TO    SECONDARY    SEXUAL    CHARACTERS.  60 

Most  of  the  wild  species  of  the  genus  (of  which  about  12  are  recognized  i 
have  horns  in  both  sexes,  but  larger  in  the  male.  There  are  'A  wild 
species  in  which  the  horns  are  lacking  in  the  female,  according  to 
Flower  and  Lydekker.  If  these  have  been  crossed  into  the  domesti- 
cated breeds  the  condition  shown  by  the  Merino  may  go  back  to  the 
wild  state.  The  third  condition  found  in  domesticated  races,  viz, 
hornlessness,  may  have  appeared  under  domestication.  Such  a  change 
might  have  arisen  in  either  of  the  two  other  types  and  would  be  com- 
parable to  well-known  losses  of  characters  shown  by  domesticated 
animals  and  plants.  These  losses  of  characters  are  usually  ascribed 
to  actual  losses  of  genes;  any  lost  gene  in  the  complex  of  factors  neces- 
sary for  the  production  of  horns  might  cause  such  a  change.  But  there 
is  no  advantage,  in  fact,  in  ascribing  the  loss  in  the  character  to  a  lost 
in  one  of  the  factors  producing  that  character,  for  any  change  of  any 
kind  in  the  factor  complex  might  bring  about  the  same  result  and  the 
evidence  from  multiple  allelomorphs  should  put  us  on  our  guard 
against  the  all  too  easy  assumption  that  a  loss  in  a  character  involves 
necessarily  loss  of  a  factor  in  the  real  sense  in  which  loss  is  used  in 
ordinary  speech. 

The  operative  and  genetic  evidence  for  sheep  shows  that  if  the  horns 
in  the  male  were  developed  through  natural  or  sexual  selection  we 
should  expect  them  to  develop  also  in  the  female.  The  greater  develop- 
ment in  the  male  seems  to  be  due  to  secretions  from  the  testes  which 
probably  are  due  to  special  factors  that  call  them  forth,  but  whether 
such  factors  were  also  acquired  to  reinforce  the  effects  being  produced 
through  selection  or  were  already  present  (reinforcement  for  horns 
being  only  a  by-product  of  their  activity)  can  not  of  course  be  known. 
We  can  suppose  that  special  factors  that  suppress  the  development  of 
horns  in  the  female  may  have  arisen  in  the  wild  or  in  the  domesticated 
races  and  have  been  perpetuated  because  of  some  imagined  benefit 
conferred;  or  that  in  certain  races  factors  were  already  present  that 
kept  down  the  development  of  horns  in  the  female.  In  any  case  such 
factors  do  not  cause  their  effects  through  secretions  from  the  ovary, 
because  after  ovariotomy  horns  do  not  develop;  nor  are  they  sex- 
linked  factors.  Any  speculation  as  to  how  natural  or  sexual  selection 
has  brought  about  the  evolution  of  the  horns  in  sheep  must  reckon 
with  the  conditions  imposed  on  such  speculation  by  the  preceding 
information.  So  far  as  I  can  see,  it  leaves  the  situation  in  this  reaped 
neither  better  nor  worse  off  than  before. 

In  deer  the  effects  of  castration  are  well  known,  but  there  is  no 
genetic  evidence  to  show  the  kind  of  factors  involved,  since  no  crosses 
have  been  made  between  species  with  differences  in  their  horns.  If  t  he 
young  male  deer  is  castrated  before  the  antlers  have  appeared,  no  horn- 
develop.  If  castrated  at  the  time  when  the  antlers  have  begun  to 
develop,  incomplete  or  imperfect  development  follows.    The  antlen 


70  THE    GENETIC   AND   THE    OPERATIVE   EVIDENCE 

remain  covered  with  the  velvet,  and  are  said  not  to  be  thrown  off 
periodically  as  in  the  normal  male.  If  the  adult  stag  with  antlers  is 
castrated,  the  horns  are  precociously  dropped,  and,  if  replaced  at  all, 
the  new  antlers  are  imperfect  and  are  not  renewed.  I  do  not  know  of 
any  cases  in  which  females  have  been  spayed,  but  no  doubt  the  ovaries 
must  sometimes  become  diseased.  There  are,  however,  a  few  records 
of  horns  developing  in  this  sex  in  old  age,  or  presumably  after  disease 
of  the  ovaries.  Both  male  and  female  reindeer  are  horned.  Castration 
produces  no  effect  on  the  development  of  the  horns. 

In  the  case  of  deer  it  is  evident  that  the  presence  of  the  testes  in  the 
male  causes  the  horns  to  develop.  The  genetic  factor,  or  factors,  for 
horns  may  be  supposed  to  be  carried  by  both  sexes,  but  the  effects  of 
the  factor  can  be  seen  only  when  the  testes  are  present.  In  the  reindeer 
and  eland,  on  the  other  hand,  the  genetic  factor  for  sex  can  produce 
horns  without  the  need  of  the  environment  produced  by  the  testes.1 
Whether  we  are  dealing  here  with  the  same  factor  or  whether  the  rest 
of  the  hereditary  complex  makes  the  result  different  can  not  be  known 
without  breeding  experiments. 

There  is  apparently  a  connection  between  the  stage  of  development 
of  the  horns  and  the  age  of  the  animal,  as  the  following  statement  by 
Yarrell2  (1858)  indicates: 

"The  fallow-buck  is  at  his  best  in  his  sixth,  or  at  most  in  his  seventh  year; 
after  which,  though  the  carcass  may  increase,  the  horns  become  smaller,  and 
irregularly  going  back  annually  through  something  like  their  former  stages  of 
increase,  a  very  old  buck  has  from  the  state  of  his  horns  been  mistaken  for  a 
young  one.  In  the  osteological  department  of  the  Museum  at  Paris  there 
was,  and  may  be  now,  the  skeleton  of  a  female  reindeer  in  which  the  horns  were 
reduced  to  little  more  than  a  rudiment  of  the  beam  and  the  brow-antler;  this 
animal  was  so  old  that  the  molar  teeth  were  worn  down  to  the  edges  of  the 
alveolar  cavities." 

At  first  sight  these  results  in  the  fallow  deer  appear  to  be  only  an  age 
condition,  but  since  in  old  age  a  reverse  process  sets  in,  it  may  appear 
more  probable  that  the  amount  of  secretion  by  the  testes  or  other 
glands  may  be  the  conditioning  agent.  In  the  case  of  the  reindeer  one 
may  hesitate  to  ascribe  the  change  to  the  ovary  without  further 
evidence. 

In  cattle  the  effects  of  castration  as  seen  in  oxen  have  been  studied. 
There  is  little  here  that  is  useful  for  our  present  purpose.  The  horns 
are  not  inhibited  and  may  even  be  larger  than  in  the  bull.  The  absence 
of  horns  in  certain  races  of  cattle  is  apparently  a  dominant  character, 
but  as  the  character  is  neither  sex-limited  nor  sex-linked,  the  evidence 
has  no  further  bearing  on  the  present  topic. 

1  In  the  eland  as  well  as  in  the  reindeer,  in  which  both  sexes  have  horns  that  begin  in  the  latter 
at  least  to  develop  before  the  gonads  ripen,  it  is  stated  that  castration  does  not  prevent  the  devel- 
opment of  the  horns  in  the  male,  but  whether  they  are  as  large  as  in  the  normal  male  is  apparently 
not  definitely  stated. 

2  Yarrell  also  states  that  after  the  fallow  buck  has  reached  the  height  of  its  maturity  and 
has  6  prongs  in  its  antler,  removal  of  one  testis  causes  the  next  antler  to  have  but  5  prongs. 


RELATING   TO   SECONDARY   SEXUAL   CHARACTERS.  71 

The  effect  of  removal  of  the  ovary  from  female  calves  has  Keen 
studied  by  Tandler  and  Keller.    The  height  of  the  ovariotamiied  female 

is  less  than  that  of  the  cow.  The  same  difference  is  found  bet  ween  bull 
and  ox.  Tandler  and  Keller  call  attention  to  the  similarity  of  t  he  head 
in  male  and  female  lacking  the  gonads.  They  conclude  that  the 
ovariotomized  female  does  not  come  to  resemble  the  male,  but  that 
removal  of  the  gonad  causes  both  sexes  to  converge  to  a  common  type. 

Castration  is  frequently  performed  in  horses,  dogs,  and  cats,  but  as 
the  secondary  sexual  differences,  aside  from  size  and  behavior,  are  not 
very  well  marked  in  these  animals,  the  results  need  not  be  here  con- 
sidered. 

Steinach's  experiments  with  rats  are  important,  because  by  grafting 
ovarian  tissue  into  the  castrated  male,  the  male  was  caused  to  assume 
certain  characteristics  peculiar  to  the  female.  The  mammary  glands 
that  are  rudimentary  in  the  male  became  much  enlarged — not  only 
the  glandular  tissue  increased  in  amount,  but  the  mammae  themselves 
were  greatly  developed.  The  hair  of  the  male  is  coarser  than  that  of 
the  female.  In  the  feminized  male  the  hair  was  soft  like  that  of  the 
female.  The  size  was  smaller  than  that  of  the  male.  The  skeleton  also 
was  affected,  and  Steinach  thinks  that  it  changed  in  the  direction  of  a 
female  skeleton.  Even  more  striking  was  the  sexual  behavior  of  the 
feminized  rat.  The  individual  no  longer  reacted  as  male,  but  showed 
some  of  the  reflexes  peculiar  to  the  female.  These  results,  that  stand 
almost  alone,  appear  to  show  that  several  of  the  secondary  sexual 
characters  of  the  female  rat  are  due  directly  to  the  presence  of  the 
ovary. 

One  of  the  most  striking  and  definite  results  shown  by  castrated 
rats  (Steinach),  guinea-pigs  (Pirsche,  Steinach),  rabbits  (Pauneet), 
hedgehog  (Marshall),  and  man  is  to  be  seen  in  the  effect  on  the  M» 
sory  glands  connected  with  the  male  ducts  as  well  as  on  the  penis. 
These  remain  small  and  infantile.  Some  substances  produced  by  the 
testes  are  essential  for  the  development  of  these  parts.  Natural 
selection  rather  than  sexual  selection  would  be  the  agency  that  here 
comes  into  play. 

In  man  the  effects  of  castration  have  been  often  described.  Kunuchs 
have  had  a  commercial  value  in  some  countries,  as  in  Turkey  :uul 
China,  and  castration  has  been  deliberately  practiced  on  young 
children.  Certain  religious  sects,  such  as  the  Skops  of  Russia,  have 
advocated  and  carried  out  the  operation.  Disease  has  also  at  times 
necessitated  the  removal  of  the  testis,  more  often  in  adults  than  in  the 
young.  The  full  effects  are  shown  only  when  the  operation  has  been 
carried  out  before  the  secondary  sexual  characters  have  developed 
The  more  striking  difference  between  the  sexes  involve  the  heard,  and 
the  hair  on  other  parts  of  the  body,  the  voice,  the  shape  of  bh*  pelvis. 
and  the  mammary  glands.  For  a  detailed  account  of  the  results. 
the  publications  of  Tandler  and  Grosz  and  Marshall's  book  on  the 
"Physiology  of  Reproduction"  should  be  consulted. 


72  THE    GENETIC   AND    THE    OPERATIVE   EVIDENCE 

The  two  most  obvious  changes  in  the  eunuch  are  the  absence  oi  the 
beard  and  mustache  and  the  small  larynx,  which  produces  a  high- 
pitched  voice.  In  both  these  respects  man  differs  from  woman;  in 
both,  however,  the  eunuch  is  like  the  boy  as  much  as  he  is  like  the 
woman.  It  is  not  evident,  therefore,  whether  the  eunuch  has  retained 
the  juvenile  condition  or  has  become  more  like  the  female.  Moreover, 
there  is  the  possibility  that  there  is  no  difference  in  the  present  case 
between  these  two  conditions.  The  distribution  of  hair  on  the  pubis 
of  the  eunuch  is  often  said  to  be  more  like  that  in  the  woman  than  that 
in  the  man,  but  there  is  apparently  no  sufficient  evidence  to  show  that 
this  is  more  than  the  juvenile  condition  or  an  undeveloped  condition 
of  the  male.  As  to  the  voice,  there  is  no  way  of  determining  whether 
the  voice  of  the  eunuch  is  feminine  or  juvenile.  The  development  of 
the  mammae  in  the  eunuch  would  be  a  better  test,  but  it  does  not  appear 
from  theliterature  on  the  subject  that  the  mammary  glands  and  the 
nipples  of  the  eunuch  are  changed  toward  the  female  type.  On  the 
contary,  it  appears  rather  that  there  is  no  such  change.  It  is  true  that 
the  tendency  toward  the  accumulation  of  fat  may  give  the  eunuch  a 
somewhat  feminine  appearance  (since  one  of  the  foci  of  fat  accumula- 
tion is  in  the  region  of  the  breasts),  but  this  in  itself  can  scarcely  be 
claimed  to  be  feminization,  but  due  rather  to  the  more  slothful  habit  of 
the  eunuch  that  tends  to  obesity. 

A  more  suggestive  resemblance  is  found  in  the  narrowness  of  the 
shoulder  girdle  and  broadness  of  the  hips  in  the  eunuch,  but  even  these 
rsemblances  to  the  female  should  be  regarded  skeptically,  since  other 
changes  in  the  bones  that  result  from  castration  are  certainly  not  a 
development  toward  the  female  type,  but  a  peculiar  specific  effect  of 
the  absence  of  testes  on  the  growth  of  the  bones.  For  instance,  the 
bones  of  the  arms  and  legs  are  much  longer  in  the  eunuch  than  in 
either  the  normal  man  or  woman,  in  fact,  more  in  the  direction  of  the 
male,  who  has  longer  legs  than  the  female.  The  explanation  usually 
given  is  that  the  ossification  at  the  ends  of  the  bones  and  of  the  epiphyses 
does  not  take  place  so  soon  as  in  normal  men  and  women.  The  con- 
dition here  is  that  characteristic  of  the  juvenile  state  that  is  carried 
over  into  the  adult,  but  whether  the  narrowness  of  the  chest  and 
shoulder  girdle  of  the  eunuch  is  correlated  in  some  way  with  the  more 
prolonged  growth  of  the  other  bones  has  not,  so  far  as  I  know,  been 
determined.  That  there  is  no  apparent  connection  between  the 
shortness  of  the  one  and  the  greater  length  of  the  other  does  not 
necessarily  lead  to  the  conclusion  that  there  is  no  such  connection. 
For  the  present  I  think  we  must  hold  this  point  in  reserve. 

Steinach's  evidence  for  the  feminized  rats,  if  it  may  be  extended  to 
man,  indicates  that  some  of  the  female  characteristics  are  due  to  the 
presence  of  the  ovary  holding  in  check  the  genetic  possibilities  of  the 
female,  as  well  as  leading  to  the  development  of  such  characteristic 


RELATING   TO    SECONDARY    SEXUAL    CHARACTERS.  7^ 

traits  as  the  mamma?,  etc.  In  the  case  of  the  pelvis  the  female  departs 
from  the  juvenile  type  of  both  sexes,  and  here  one  might  look  for 
a  better  criterion.  It  is  stated  that  the  pelvis  of  the  ox  is  more  like 
that  of  the  female  than  it  is  like  that  of  the  male,  and  it  lias  been  said 
that  this  is  true  for  the  castrated  rat  and  guinea-pig,  but  whether  a 
simple  enlargement  of  the  juvenile  pelvis  would  make  it  resemble  the 
female  type  more  than  that  of  the  male  has  not,  so  far  as  I  know,  been 
carefully  examined.  Should  it  prove  here  that  this  is  the  case,  the 
evidence  on  this  point  would  be  no  stronger  than  that  for  other  charac- 
ter  differences.  As  has  been  stated,  Tandler  and  Grosz  think  that  the 
changes  in  the  skeleton  of  the  ox,  as  well  as  those  in  the  castrated  cow 
(skull,  pelvis,  and  limb  bones),  are  due  directly  to  loss  of  the  gonads 
and  are  much  the  same  in  both.  But  their  resemblance  may  possibly 
be  due  more  to  an  enlarged  juvenile  condition  rather  than  that  either 
of  them  changes  toward  the  normal  skeleton  of  the  other  sex. 

The  statements  that  have  been  published  concerning  the  effects  of 
removal  of  the  ovaries  in  woman  are,  on  the  whole,  unsatisfactory  and 
often  contradictory.  That  the  uterus  and  oviducts  become  smaller  is 
expected  from  what  is  known  to  occur  in  other  mammals,  and  is 
definitely  recorded  in  the  human  female.  That  the  breasts  become 
smaller  is  stated  to  be  the  case,  but  whether  because  of  an  actual 
decrease  in  the  glandular  portion  has  not,  so  far  as  I  know,  been 
shown.  That  hair  is  likely  to  develop  on  the  upper  lip  of  woman 
without  ovaries  is  also  claimed  as  likely  to  occur,  and  this,  too,  is 
sometimes  seen  in  old  women,  but  if  it  is  interpreted  to  mean  an 
approach  to  the  bearded  condition  of  man  it  should  be  admitted  that 
the  development  is  hardly  sufficient  to  invite  such  a  comparison. 
Finally,  it  has  been  stated  that  the  voice  becomes  deeper,  more,  there- 
fore, like  the  male,  but  this  has  also  been  denied.  If  it  could  be 
established  that  the  voice  changes  and  that  it  was  brought  about  by 
an  enlargement  of  the  larynx,  similar  to  that  which  takes  place  when 
the  larynx  of  the  boy  changes  to  that  of  the  man,  it  might  seem  not 
improbable  that  the  change  was  toward  that  of  the  opposite  Bex 
This  would  mean  that  the  ovary  produces  some  substance  that  pre- 
vents the  enlargement  of  the  larynx  in  the  female.  But  since  it  has 
been  shown  that  the  enlargement  in  the  male  is  caused  by  the  develop- 
ment of  the  testes,  and  that  this  enlargement  is  prevented  by  east  rat  i<  m, 
a  paradoxical  situation  would  present  itself,  viz,  that  the  testes  cause 
the  larynx  to  enlarge  in  the  male  and  the  ovary  prevents  the  enlai 
ment  in  the  female.  Until  convincing  evidence  is  forthcoming,  the 
question  is  better  left  undecided. 

B.  Evidence  from  Birds. 

Probably  a  greater  difference  in  the  secondary  sexual  characters  is 
shown  in  birds  than  in  any  other  group.     It   is  true  that   there  are 


74  THE    GENETIC   AND   THE    OPERATIVE   EVIDENCE 

species,  such  as  the  doves  and  pigeons,  in  which  the  plumage  of  the 
male  is  much  like  that  of  the  female,  but  this  is  the  exception  rather 
than  the  rule.  At  the  other  extreme  are  species  like  birds  of  paradise, 
hummingbirds,  fowls,  pheasants,  ducks,  and  many  passerines,  in 
which  the  plumage  of  the  two  sexes  is  entirely  different.  Our  knowledge 
as  to  the  relation  between  the  nuptial  plumage  of  the  male  and  the 
condition  of  the  sex-organs  rests  largely  on  information  gained  by 
castration  in  poultry  and  ducks  and  on  the  assumption  of  the  nuptial 
plumage  in  several  species  only  at  the  mating  season. 

John  Hunter  in  1780  described  a  pheasant  with  male  plumage.  His 
account  of  a  similar  change  in  a  pea  fowl  is  so  complete  that  I  venture 
to  quote  it  in  full: 

"Lady  Tynte  had  a  favorite  pyed  pea-hen,  which  had  produced  chickens 
eight  several  times;  having  moulted  when  she  was  about  eleven  years  old,  she 
astonished  the  lady  and  her  family  by  showing  the  feathers  peculiar  to  the 
other  sex,  and  appearing  like  a  pyed  peacock.  In  this  process  the  tail,  which 
was  similar  to  that  of  a  cock,  first  appeared  after  moulting.  In  the  following 
year  she  moulted  again,  and  produced  the  same  feathers.  In  the  third  year 
she  did  the  same;  at  the  same  time  she  had  spurs  similar  to  those  of  a  cock. 
She  died  in  the  following  winter  during  the  hard  frost,  namely,  in  the  winter 
1775-6.  She  never  bred  after  this  change  in  her  plumage.  This  bird  is  now 
preserved  in  the  Museum  of  Sir  Ashton  Lever."  l 

"From  what  has  been  related  of  these  two  birds,  may  it  not  reasonably  be 
inferred  that  it  seems  probable  that  all  those  wild  pheasants  of  the  female  sex, 
which  are  found  with  the  feathers  of  the  cock,  had  changed  the  nature  of  their 
feathers,  particularly  at  a  certain  age? 

"  If  this  idea  be  just,  it  shews  that  there  is  a  disposition  in  the  female  to  come 
nearer  and  nearer  to  the  male,  at  least  in  the  secondary  properties;  or  it  may 
rather  be  said  that  the  female  is  later  in  producing  this  change  than  the  male  is; 
for  it  has  already  been  observed  that  both  sexes  when  young  differ  not  from 
each  other  in  these  respects,  but  that  the  male  appears  to  be  the  one  that  by 
degrees  separates  from  the  female  in  its  secondary  properties." 

Statements  in  regard  to  the  effect  of  castration  on  poultry  go  back, 
it  appears,  to  Aristotle.  Yarrel  in  1811  and  again  in  1850  has  given  an 
excellent  account  of  many  of  the  effects  produced.  His  account  of  the 
effects  on  the  cock  seem  to  be  based  partly  on  hearsay,  and  while  they 
contain  much  accurate  information,  yet  the  statement  that  the 
plumage  of  the  capon  is  intermediate  between  that  of  the  cock  and  hen 
is  incorrect.  The  further  statement  that  by  cutting  the  oviduct  the 
hen  assumes  the  plumage  of  the  capon  has  been  shown  by  Sellheim  to 
be  erroneous.  The  operation  referred  to  by  Yarrel  must  have  been 
one  in  which  the  ovary  was  removed. 

1  It  might  be  supposed  that  this  bird  was  really  a  cock  which  had  been  changed  for  a  hen;  but 
the  following  facts  put  this  matter  beyond  a  doubt:  First,  there  was  no  other  pyed  pea-fowl  in 
the  country.  Secondly,  the  hen  had  knobs  on  her  toes,  which  were  the  same  after  her  change. 
Thirdly,  she  was  as  small  after  the  change  as  before,  therefore  too  small  for  a  cock.  Fourthly,  she 
was  a  favorite  bird,  and  was  generally  fed  by  the  lady,  and  used  to  come  for  her  meat,  which 
she  still  continued  to  do  after  the  change  in  the  feathers. 


RELATING    TO    SECONDARY    SEXUAL    CHARACTERS.  75 

Yarrel  described  a  female  pheasant  that  had  assumed  some  of  tho 
characteristic  colors  of  the  male.  On  dissection  he  found  that  the 
ovary  was  diseased  as  well  as  the  oviduct.  He  correctly  assigns  the 
change  in  plumage  to  the  condition  of  the  ovary.  He  states  further- 
more that  most  of  the  female  pheasants  that  he  had  examined  t  hat  had 
male  plumage  had  not  assumed  the  complete  coloration  of  the  male 
In  one  case,  however,  a  complete  change  had  taken  place.  The  change 
in  pheasants  he  thought  was  due  to  old  age  accompanied  by  partial 
or  complete  loss  of  function  of  the  ovary.    For  poultry  he  stat 

"In  the  imperfect  female  the  comb  increases;  a  short  spur  or  spurs  appear; 
the  plumage  undergoes  an  alteration,  getting  what  is  usually  called  'foul- 
feathered;'  she  ceases  to  produce  any  eggs,  and  makes  an  imperfect  attempt  to 
imitate  the  crow  of  the  cock.  Being  profitless  in  this  state,  she  is  usually  made 
away  with.     The  proverb  says : 

A  whistling  woman  and  a  crowing  hen 
Are  neither  good  for  gods  nor  men. 

Our  neighbors  and  allies  the  French,  who  seem  to  take  a  wider  range  in  their 
prejudice  against  habits  which  they  consider  irregular,  have  the  following 
proverb,  which  says: 


Poule  qui  ehante,  Pretre  qui  danse 
Et  Femme  qui  parle  latin, 
N'arrivent  jamais  a  belle  fin. 


"I  have  seen  two  instances  in  which  females  of  the  wild  duck  have  assumed 
to  a  considerable  extent  the  appearance  of  the  plumage  of  the  mallard,  even  to 
the  curled  feathers  of  the  tail.  One  of  these  birds,  in  my  own  collection,  was 
given  me  when  alive  by  my  kind  friend  the  late  John  Morgan,  esq.  When  this 
bird  was  examined  after  death,  the  sexual  organs  were  found  to  be  diseased,  as 
in  the  case  of  the  hen  pheasants  referred  to,  and  figured  in  the  2d  volume  of  the 
History  of  our  British  Birds.  In  the  published  illustrations  to  his  Fauna  of 
Scandinavia,  M.  Nilsson  has  given  a  colored  figure  of  a  duck  in  this  state  of 
plumage  (plate  163),  which  is  called  a  barren  female,  and  in  which  the  curled 
tail-feathers  are  made  very  conspicuous. 

"From  the  general  similarity  in  these  females  to  the  appearance  assumed 
for  a  time  by  healthy  males  in  July,  I  am  disposed  to  refer  this  seasonal  change 
in  males,  in  this  and  in  other  species  of  ducks,  to  a  temporary  exhausted  state 
of  the  male  generative  organs,  and  their  consequent  diminished  constitutional 
influence  on  the  plumage. 

"A  male  shut  up  by  himself  from  early  spring  to  the  end  of  July  undergoes 
no  change  in  his  plumage;  but  if  he  is  allowed  to  associate  with  females  till 
their  season  of  incubation  commecnes,  he  then  goes  through  the  change,  and 
this  appears  to  indicate  the  cause  of  the  partial  summer  moulting. 

"The  appearance  is  somewhat  different,  but  yet  very  interesting  in  insects 
and  Crustacea.  In  these  classes  the  sexual  organs  are  double  and  distinct, 
arranged  one  on  each  side  of  the  elongated  mesial  line.  It  sometimes  happens, 
that  a  species  in  which  the  sexes  are  of  a  different  color,  or  markings,  or  form 
has  one  sexual  organ  of  each  sort,  male  and  female,  in  which  case  each  half 
of  the  same  insect  is  developed  under  the  exclusive  influence  of  the  sexual  organ 
on  its  own  side.  Instances  are  preserved  among  our  collect ionfl  of  buttert! 
mothes  and  beetles;  and  I  have  seen  it  twice  in  the  common  lobster. 


76       THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

"Nor  is  the  human  race  exempt  from  the  operation  of  the  law  which  prevails 
in  the  Mammalia.  In  women,  at  an  advanced  age,  hair  appears  on  the  chin 
and  upper  lip,  and  the  voice  alters,  becoming  deep  in  its  tone.  The  beard  in 
old  men  becomes  thin  and  soft,  and  our  own  inimitable  Shakespeare  has  told  us, 

*  *  *  his  big  manly  voice 
Turning  again  toward  childish  treble,  pipes 
And  whistles  in  his  sound. 

Gurney  (1888)  has  recorded  several  cases  in  which  female  birds 
have  assumed  male  plumage.  For  instance,  he  describes  a  female 
merganser,  Mergus  serrator,  assuming  male  plumage  that  showed  no 
signs  of  disease  in  the  ovary.  Mr.  Cecil  Smith  had  a  female  widgeon 
(Mareca  penelope)  on  his  ponds  near  Trenton,  which  assumed  the  male 
plumage  some  years  ago,  and  which,  so  far  as  he  knew,  had  not  had 
young  nor  laid  eggs. 

"On  May  16th,  1887,  a  chaffinch  (Fringilla  Calebs)  in  full  male  plumage  was 
shot  at  Chapel  Town,  near  Leeds,  in  Yorkshire,  by  the  son  of  Mr.  W.  L.  Jack- 
son, M.  P.;  it  was  skinned  by  G.  R.  Grassham,  assistant  to  Mr.  W.  E.  Clarke 
at  the  Museum,  who,  much  to  his  surprise,  found  that  it  was  a  female,  and 
contained  an  egg,  ready  for  laying,  of  a  pale  blue,  without  markings,  and  an- 
other egg  in  a  less  forward  state.  This  chaffinch  is  in  every  way  in  perfect 
male  plumage,  and  I  am  indebted  to  Mr.  Clarke  for  his  kindness  in  sending 
these  particulars  with  the  specimen,  which  he  received  from  Grassham  a  few 
hours  after  the  latter  had  dissected  the  bird. 

"In  the  'Norwich  Nat.  Trans.,'  an  enumeration  was  given  of  female  Red- 
starts (Ruticilla  phoenicurus)  assuming  male  plumage  (I.  c.)  to  which  the  fol- 
lowing may  be  added:  a  hen  R.  phoenicurus  assuming  male  plumage,  and  very 
like  Mr.  Millais'  described  in  the  'Norwich Nat.  Trans.'  iv., p.  182,  was  caught 
by  Mr.  W.  E.  Clarke  sitting  upon  her  eggs,  at  Wike,  near  Leeds,  in  June,  1886; 
at  the  same  time  Mr.  Clarke  saw  the  cock  close  by,  which  appeared  to  be  in  the 
ordinary  male  plumage.  The  late  Mr.  Henry  Doubleday's  collection  con- 
tained a  hen  Redstart  (R.  phoenicurus)  in  male  plumage,  which  had  the  ovaries 
'quite  perfect  and  full  of  eggs'  (cf.  B.  of  Norf.,  i,  p.  370,  note),  probably  one  of 
those  alluded  to  by  Yarrell  (Brit.  B.  1st  ed.  i,  p.  240)  in  the  remarks  made  by 
him  on  the  plumage  of  this  species.  I  have  some  recollection  of  this  Redstart 
at  the  dispersal  of  Mr.  Doubleday's  collection,  but  do  not  know  who  was 
the  purchaser  of  it.  There  can  be  no  doubt  that  more  would  soon  turn 
up  if  looked  for;  and  now  that  attention  has  been  drawn  to  the  subject, 
and  the  practice  of  dissection  is  getting  more  general  among  bird  stuffers,  it  is 
certain  to  be  the  case,  not  only  in  Ruticilla,  but  in  other  genera  besides.  Why 
it  should  happen  in  Ruticilla  phoenicurus  oftener  than  in  other  Passerine  birds 
is  hard  to  explain,  but  such  is  evidently  the  case." 

"The  same  is  recorded  to  have  happened  five  or  six  times  with  the  female 
Red-backed  Shrike  (Lanius  colluria);  see  'the  Field,'  June  17,  1871,  and  April 
25,  1885;  Mag.  N.  H.,  iv,  p.  344;  'B.  of  Suffolk,'  p.  45;  'Ibis,'  1863,  p.  292;  but 
the  number  of  hen  Redstarts  which  have  donned  masculine  attire  is  greater. 

"The  following  is  a  list  of  the  species  in  which  one  or  more  instances  of 
females  assuming  male  plumage  are  ascertained  to  have  occurred : 

Falco  aesalon,  fide  Scully.     (Cf.  Sharpe,  'Cat.  Birds  Brit.  Mus./  i,  p.  407). 

Tinnunculus  alaudarius,  fide  Sharpe;  col.  fig.  P.  Z.  S.,  1874,  p.  580. 

Lanius  collurio,  fide  Hoy. 

Lanius  vittatus,  fide  Blyth. 

Ruticilla  phoenicurus,  fide  Millais,  Clarke  and  others. 


RELATING   TO    SECONDARY    SEXUAL   CHARACTERS.  77 

Fringilla  coolebs,  fide  Clarke. 

Linota  cannabina,  fide  Blyth. 

Linota  rufescens,  fide  Blyth. 

Nectarinia  asiatica,  fide  Blyth. 

Gallus  (domestic  fowl),  fide  Yarrell  and  others;  col.  fig.  "B.  of  Sherwood,"  p.  183. 

Pavo  (peahen),  fide  Latham;  fig.  "Synopsis,"  ii,  pi.  60. 

Meleagris  (Turkey),  fide  Bechstein. 

Phasianus  colchicus,  fide  Edwards  and  others.  Of  common  occurrence  in  a  semi- 
domesticated  state. 

Thaumalea  picta,  fide  Edwards. 

Euplocamus  nycthemerus,  fide  Yarrell. 

Pucrasia  nipalensis,  fide  Blyth. 

Tetrao  tetrix,  fide  Bond;  col.  fig.  Dresser,  "B.  of  Eur.,"  vi,  205. 

Tetrao  urogallus,  fide  Nilsson;  col.  fig.  "Unser  Auer-,  Rackel-  und  Birkwild  und 
seine  Abarten,"  by  A.  B.  Meyer. 

Otis  tarda,  fide  Tiedmann. 

Anas  (domestic  duck),  fide  Rowley;  col.  fig.  "Orn.  Misc.,"  i,  p.  118. 

Anas  boschas,  fide  Hancock;  fig.  col.  " Scandinavisk  Fauna,"  pi.  163. 

Fuligula  marila,  fide  Blyth;  see  also  P.  Z.  S.,  1885,  p.  246. 

Mergus  serrator,  fide  Gurney. 

Mareca  penelope,  fide  Cecil  Smith. 

"Perhaps  the  Kestrel  (Tinnunculus  alaudarius)  ought  not  to  be  included 
in  this  catalogue,  for  so  many  have  been  seen  with  the  lower  part  of  the  back 
blue  or  bluish,  as  to  leave  little  doubt  that  the  female  generally  becomes  so  if 
she  lives  long  enough. 

"It  is  said  that  the  females  in  Oriolus  generally  become  as  bright  as  males  in 
time  ('Ibis/  1864,  p.  412;  'Field,'  June  24th  and  July  8th,  1871)." 

"P.  S. — Mr.  W.  Tegetmeier  tells  me  he  has  known  a  barnyard  cock  moult 
into  hen's  plumage,  which  is  the  converse  of  the  instances  narrated  in  this 
paper,  and  rather  resembles  the  annual  change  which  takes  place  in  Anas 
boschas  and  others  of  that  tribe." 

In  a  later  notice  Gurney  makes  the  following  statement : 

"The  bearded  tit  {Panurus  biarmicus)  may  be  added  to  the  list  of  female 
birds  which  are  known  to  occasionally  assume  male  plumage.  In  the  summer 
of  1882  a  bearded  tit,  two  years  old,  in  Mr.  J.  G.  Keulemans'  aviary,  hatched 
five  eggs  and  moulted,  during  which  operation  she  suffered  much  from  cold 
and  stiffness,  and  when  she  recovered  her  plumage  it  was  partly  that  of  the 
male  (c/.  'The  Field,'  Sept.  14,  1872)." 

Brandt,  who  has  reviewed  the  literature  very  thoroughly,  cites  the 
following  cases: 

"Galeinacei:  Gallus  bankiva  domest.,  Phasianus  pictus,  torquatus,  col- 
chicus, mongolicus  and  nycthemerus,  Pavo  cristatus  domost.,  Meleaeris  gallo- 
pave  domest.,  Perdix  einerea,  Tetrao  urogallus,  tetrix  und  bonasia. 

"Passeres:  Fringilla  coelebs,  Pyrrhula  vulgaris,  coccinea,  Loxia  chlons, 
Turdus  merula,  Ruticilla  phoenicurus,  ochrura,  chryaogastra,  ("vallecula 
Wolfii,  Sturnus  vulgaris,  Ampelis  cotinga. 

"Scansores:  Cuculus  canorus,  Edolius  glandarius. 

"  Grallatores :  Machetes  pugnax. 

"Natatores:  Anas  boschas  domest. 

"Es  ware  denkbar,  dass  die  Hahnenfedrigkeit,  wenn  audi  in  verkapptem 
Grade,  alien  Vogeln,  selbst  denjenigen  zukomme,  deren  Gefieder  una  gea- 
chlechtlich  uniform  zu  sein  scheint,  Wie  dem  auch  sei.  cinzelne  Genera  und 
Species  scheinen  mehr,  andere  weniger  zur  Arrhenoidie  pnidisponirt. 


78  THE    GENETIC   AND   THE   OPERATIVE   EVIDENCE 

bemerkt  J.  Geoffroy  St.  Hilaire  (p.  511),  dass  Fasanen  haufiger  selbst  als  die 
Hiihner  hahnenfedrig  werden,  wahrend  fur  den  Pfau,  den  man  doch  stets  eines 
naturlichen  Todes  sterben  lasst,  ihm  nur  ein  einziger  Fall  (der  von  Hunter) 
bekannt  geworden.  Wahrend  Lorenz  (vide  Tichomirow)  auf  dem  Moskauer 
Markt  haufiger  hahnenfedrige  Weibchen  von  Phasianus  colchicus  und  mongol- 
icus  aufgefunden,  ist  ihm  dieses  fur  Ph.  chrysomelas  bisher  kein  einziges  Mai 
gelungen,  obgleich  die  Zahl  der  jahrlich  in  Moskau  feilgebotenen  Exemplare 
dieser  Art  sich  auf  8000  Stuck  belaufen  mochte." 

The  preceding  cases  relate  to  exceptional  changes  in  the  plumage  as 
observed  in  nature,  or  in  birds  kept  under  domestication.  We  may  next 
examine  the  cases  where  the  ovary  or  the  testis  has  been  removed. 

The  earlier  observations  of  Berthold,  Wagner,  Hanau,  Samuel, 
Sellheim,  Pirsche,  Foges,  Shattock,  and  Seligman  are  sufficiently 
covered  by  later  work  quoted  below.  Sellheim's  work,  however,  is 
especially  to  be  noted,  since  he  gives  some  measurements  covering  the 
weight  of  the  brain,  heart,  and  body  of  the  cock  and  capon,  as  well 
as  observations  on  the  skull  and  skeleton.  The  weight  of  the  brain 
is  slightly  less  in  the  capon,  but  the  body-weight  is  greater.  He  ques- 
tions whether  the  ovary  has  ever  been  successfully  removed,  and  he 
shows  that  the  operation  of  resecting  the  oviduct  does  not,  as  was 
supposed,  lead  to  the  degeneration  of  the  ovary.  On  the  contrary,  he 
found  that  after  the  effects  of  the  operation  had  been  removed  the 
ovary  began  again  its  functions. 

From  Goodale's  careful  summing  up  of  the  effects  of  castration  only 
the  following  points  need  be  recalled:  The  feathers  are  little  changed; 
some  of  them,  the  hackles  especially,  become  longer.  The  lowermost 
tier  of  wing  coverts  are  elongated  as  compared  with  those  of  the  cock. 
The  spurs  are  practically  the  same  in  the  capon  and  cock.  The  capon 
is  disinclined  to  give  voice,  but  at  times  he  crows.  The  molting  is  not 
affected.  The  size  of  the  capon  is  larger.  He  pays  little  attention  to 
the  hens.  He  is  not  pugnacious,  and  if  attacked  will  not  often  fight. 
As  a  rule  he  does  not  pursue  the  hens,  but  if  a  hen  squats  down  as  the 
capon  approaches  he  will  mount  and  go  through  the  characteristic 
mating  reaction.  The  comb  is  extremely  small,  much  smaller  than 
that  of  the  female  of  the  same  race ;  it  is  infantile  rather  than  feminine. 

Comparing  these  results  with  those  that  I  have  observed  in  the 
castrated  Sebright,  we  find  that  aside  from  the  assumption  of  the  full 
plumage  of  the  cock-feathered  bird  the  Sebright  shows  all  of  the 
characteristic  features  of  the  capon.  The  spurs  develop,  perhaps  even 
more  fully  than  in  the  normal  Sebright  cock.  He  seldom  crows,  and 
then  weakly.  The  birds  appear  large,  but  the  excessive  development 
of  the  feathers  produces  the  effect.  I  have  not  weighed  them  to  show 
whether  an  actual  increase  in  size  takes  place.  Two  of  my  birds  are 
notably  large  for  Sebrights,  but  the  others  are  smaller.  Both  large  and 
small  cocks  occur  in  the  strain  that  I  have  used.  My  Sebright  and 
other  capons  neglect  the  hens,  but  I  have  seen  them  tread  the  hens 


RELATING   TO    SECONDARY    SEXUAL    CHARACTER  79 

on  occasion.  They  will  fight  each  other,  if  two  strangers  meet .  1  >ui  the 
attacks  are  not  violent  or  prolonged.  A  normal  male  beata  them 
easily,  and  afterwards  they  run  away  from  such  birds.  The  combs  and 
wattles  are  very  small  and  pale.  If  a  piece  of  the  testis  is  left  in,  the 
comb  is  a  fair  index  of  its  size.  In  the  birds  that  changed  back  toward 
a  Sebright  the  comb  slowly  enlarged.  After  the  second  operation  it 
decreased  again  as  the  plumage  once  more  changed  to  that  of  the  cock. 

Goodale's  results  with  ovariotomized  females  are  especially  note- 
worthy, since  here  for  the  first  time  we  have  definite  information  as  to 
the  effects  of  the  operation.  By  using  a  well-established  breed,  the 
brown  Leghorn,  in  which  the  dimorphism  of  the  sexes  is  very  striking, 
the  results  are  made  all  the  more  convincing.  Goodale  found  that  it  was 
possible  to  completely  remove  the  ovary  of  young  birds,  for  at  an  early 
age  the  ovary  is  sufficiently  compact  to  make  its  entire  removal  ] 
sible.  Later  the  ovary  becomes  more  diffuse,  and  complete  removal 
is  almost  impossible.  In  a  few  successful  cases,  in  which  the  ovary 
had  been  completely  removed,  the  bird  assumed  the  full  plumage  of 
the  Leghorn  cock,  with  red  back,  black  breast,  and  long,  pointed  hackle 
and  saddle  feathers.  Spurs  developed  in  all  the  operated  females,  even 
when  the  ovary  was  not  entirely  removed.  There  can  be  little  doubt 
that  the  ovary  holds  back  the  development  of  the  spurs,  but  as  some 
hens  sometimes  develop  spurs,  especially  in  certain  breeds,  it  is  not 
entirely  certain  that  in  these  cases  the  loss  of  the  ovary  is  the  cause  of 
the  appearance.  The  comb  (and  wattles)  developed  to  different 
degrees;  in  some  birds  it  was  as  large  as  in  the  cocks,  in  others  no 
larger  than  in  the  normal  hen,  but  in  all  cases  it  was  larger  than  in  the 
capon.  What  to  conclude  is  doubtful.  Tentatively  it  may  be  suggest  ed 
that  the  genetic  complex  that  gives  the  female  (ZW)  produces  a  comb 
as  large  as  that  shown  by  the  female  independently  of  the  ovary,  but 
beyond  this  point  the  ovary  inhibits  the  further  development  of  the 
comb,  presumably  by  means  of  the  same  internal  secretion  that  holds 
down  the  cock  plumage  in  the  hen.  In  the  male,  on  the  other  hand, 
the  genetic  complex  (ZZ)  produces  a  comb  much  smaller  than  that  of 
the  female  (no  more  than  that  of  the  capon),  and  the  testes  produce  a 
substance  that  causes  this  comb  to  grow  to  the  size  of  that  of  the  eock. 
Possibly,  however,  other  internal  secretions  are  involved. 

The  operated  hens  are  quiet  and  nearly  voiceless.  None  of  Goodale  B 
birds  were  heard  to  crow,  yet  this  seems  to  be  a  well-known  peculiarity 
of  old  hens  that  have  become  cock-feathered.  The  operated  hens  are 
not  larger  than  the  normal  hens  of  the  same  breed.  Their  legs  reman) 
short,  as  in  the  normal  hen;  and  in  this  respect  and  in  size  the  ovarioto- 
mized bird  is  externally  a  female.  The  poullards  "never  visit  the 
nests,  never  sing  or  cackle,  show  none  of  the  normal  female  reactions, 
and  few  or  none  of  the  male." 


80       THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

The  influence  of  the  ovary  in  suppressing  the  cock  plumage  has  been 
convincingly  shown  in  an  experiment  of  Goodale's,  in  which,  after 
removal  of  both  testes  from  the  young  Leghorn  cock,  pieces  of  ovaries 
were  inserted  into  the  body-cavity.  As  dissection  showed  later,  several 
of  these  implanted  pieces  grew  onto  the  wall  of  the  body-cavity.  The 
birds  developed  the  plumage  of  a  hen,  although  some  traces  of  the  male 
plumage  were  at  times  present.  The  difference  between  the  sexes  is  so 
great  in  Brown  Leghorns  that  the  hen-feathering  of  the  feminized 
cockerels  leaves  no  doubt  that  the  presence  of  the  ovary  had  produced 
the  female  coloration. 

Geoffrey  Smith  and  Mrs.  Haig  Thomas  (1913)  have  examined  a 
number  of  hybrid  pheasants,  some  of  which  were  sterile.  They  found 
that  the  ovary  (and  oviduct)  was  often  small  and  degenerate.  There 
was  a  more  or  less  corresponding  tendency  for  such  female  hybrids  to 
show  male  feathering,  at  least  in  a  part  of  the  plumage.  The  degenera- 
tion of  the  sex  element,  however,  does  not  take  place  until  after  the 
time  of  synapsis,  so  that  the  younger  germ-cells  may  be  normal.  The 
later  degeneration  of  these  cells  is  not  likely  to  influence  the  secondary 
sexual  characters,  but  may  be  an  index  of  changes  in  other  parts  of 
the  ovary. 

Geoffrey  Smith  had  a  breed  of  White  Leghorns  with  cocks  of  two 
classes — those  that  assumed  cock  plumage  at  6  months,  and  those  that 
are  like  the  hens  for  8  months,  after  which  they  slowly  assume  the 
cock-feathering.  The  difference  is  hereditary  and  appears  to  segregate. 
Possibly  this  breed  had  one  factor  at  least  for  hen-feathering  that  is 
more  effective  for  young  birds  than  for  older  ones. 

Smith  states  that  birds  and  crabs  (see  infra)  appear  to  give  opposite 
results,  since  removal  of  the  ovary  in  the  former  leads  to  development 
of  secondary  male  characters  and  removal  of  testes  in  the  latter  to 
secondary  female  characters.  But  he  adds  that  he  thinks  the  results 
are  really  the  same,  because  in  the  crab  it  is  not  the  suppression  of  the 
testis  but  the  feminization  of  the  male  by  the  Sacculina  that  causes  the 
change. 

There  are  a  number  of  observations  on  ducks.  Several  cases  have 
been  recorded  where  in  old  age  the  female  assumed  the  male  plumage 
(Darwin,  Shattock,  and  Sellheim).  Also  a  few  cases  in  which  the  testes 
were  removed.  Those  of  Goodale  are  the  most  complete  and  striking. 
The  male  duck  has  two  characteristic  plumages,  one  called  the  nuptial 
also  called  the  summer  or  breeding  plumage  that  is  assumed  at 
the  molt  in  the  autumn,  and  the  other  the  eclipse  plumage,  which  is 
not  identical  with  but  much  like  that  of  the  female.  Here,  then,  we 
find  a  new  situation,  and  one  that  invites  comparison  with  the  con- 
dition in  Sebrights,  in  so  far  as  the  male  becomes  hen-feathered  at 
certain  seasons. 


RELATING   TO   SECONDARY   SEXUAL   CHARACTERS.  81 

Throughout  the  greater  part  of  the  year  the  Rouen  drake  lias  the 
nuptial  plumage.  The  head  is  green  and  the  breast  is  claret.  Two 
median  tail  feathers  are  strongly  curved;  the  next  two  are  also  often 
curved.  These  four  are  called  the  sex  feathers.  At  the  close  of  the 
breeding-season  (July)  both  sexes  molt.  The  male  now  has  the  same 
coat  as  the  female,  or  nearly  so.  The  green  head  becomes  brown  to  buff ; 
the  sex  feathers  are  straight.  The  change  back  again  to  the  nuptial 
plumage  beginsat  the  end  of  summer  and  is  completed  early  in  October. 
Thus  in  the  race  of  Rouens  the  eclipse  plumage  lasts  only  a  very  short 
time.  In  the  mallard  it  lasts  longer.  The  eclipse  plumage  develops, 
therefore,  only  when  the  testes  are  active,  or,  as  Goodale  puts  it,  "the 
presence  of  the  active  testis  is  necessary  for  the  drake  to  assume  this 
plumage."  Conversely,  the  nuptial  plumage  comes  on  in  the  late 
summer,  when  mating  is  over,  and  when  the  testes  have  shrunken  and 
are  not  active,  at  least  as  far  as  the  sex-cells  are  concerned.  In  some 
respects  the  situation  is  like  that  in  the  fowls,  for  in  both  the  testes  are 
not  necessary  for  the  development  of  the  full  plumage,  but  in  other 
respects  the  situation  is  different,  because  at  the  time  in  the  ducks 
when  the  testes  are  active  the  eclipse  plumage  develops.  Are  we  to 
suppose  that  at  the  time  of  sexual  activity  a  substance  is  produced 
analogous  to  that  produced  by  the  ovary  of  the  female?  This  seems 
the  most  plausible  assumption,  for  we  know  that  if  the  testis  is  removed 
the  eclipse  plumage  does  not  appear.  Such  a  situation  suggests  a 
comparison  with  the  Sebright,  where  it  has  been  shown  that  the  testis 
must  actively  produce  some  substance  which,  like  that  in  the  ovary, 
keeps  down  cock-feathering.  It  is  plausible,  even  if  it  can  not  be 
established,  that  the  substance  in  the  duck  and  the  inhibitory  substance 
in  the  male  Sebright  are  the  same  as  that  produced  in  the  female. 

Goodale's  results  with  females  (ducks)  are  not  so  clear  cut,  because 
the  ovariotomized  females  turned  out  to  be  of  two  sorts.  One  sort  is 
almost  identical  with  the  male,  the  other  is  more  intermediate.  There 
are  sufficient  reasons  for  thinking,  he  says,  that  these  differences  are 
not  due  to  defective  operations.  Goodale  suggests  a  genetic  difference 
in  the  females  used,  but  this  is  apparently  even  to  Goodale  himself 
not  a  very  satisfactory  solution.  For  our  present  purpose  the  impor- 
tant fact  is  that  the  ovariotomized  female  may  assume  the  perfect  male 
plumage.  Evidently  the  ovary  produces  some  substance  which,  as  in 
the  hen,  suppresses  the  potential  plumage  of  the  male.  One  such  female 
known  to  have  had  all  the  ovary  removed  never  assumed  the  summer 
(eclipse)  plumage  of  the  drake.  On  the  other  hand,  another  female 
developed  first  the  nuptial  plumage,  but  this  was  replaced  by  the 
summer  coat  "of  the  male  of  this  variety."  Again,  in  the  summers  *A 
1914  and  1915  the  change  to  the  eclipse  plumage  was  followed  in  the 
autumn  by  a  return  to  the  nuptial  plumage. 


82       THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

How  can  we  explain  the  apparent  discrepancy  of  Goodale's  results? 
In  one  case,  the  nuptial  plumage  was  molted  to  nuptial  plumage;  in 
the  other  case  an  eclipse  plumage  appeared  at  the  breeding-season. 
Goodale  regards  the  latter  case  as  a  more  perfect  approach  to  the  male 
than  the  former,  but  this  view  undoubtedly  offers  serious  theoretical 
difficulties.  It  seems  to  me  possible  to  suppose  that  in  those  cases 
where  the  summer  plumage  appeared  there  was  in  reality  enough 
ovarian  tissue  (or  related  tissue)  left  after  the  operation  to  produce  an 
effect  at  the  normal  season  for  such  ovarian  tissue  to  become  most 
active.  It  might  then  suffice  to  eclipse  the  male  plumage  sufficiently 
to  make  it  very  similar  to  the  eclipse  of  the  normal  male.  At  any  rate, 
on  this  basis  we  have  a  consistent  explanation  of  the  entire  complex 
of  phenomena. 

What  bearing  have  these  results  relating  to  castration  and  trans- 
plantation on  the  theory  of  sexual  selection?  Granting,  of  course,  that 
selection  takes  the  materials  as  it  finds  them,  there  may  still  be  restric- 
tions imposed  on  the  theory  by  the  kind  of  material  offered.  For 
instance,  the  development  of  the  plumage  of  the  cock  is  independent 
of  the  condition  of  his  testes.  Hence,  if  the  female  selected  the  more 
vigorous  male,  she  would  not  necessarily  obtain  one  more  ornate  than 
his  less  vigorous  rivals.  If  the  taste  of  the  hen  has  built  up  the  plumage 
of  the  cock,  it  has  been  carried  out  then  independently  of  the  vigor 
resulting  from  the  greater  activity  of  the  testis.  In  a  word,  the  more 
vigorous  male  is  not  necessarily  the  most  highly  colored  one.  Darwin 
concedes  that  these  two  conditions,  high  color  and  vigor,  must  go 
together  to  insure  success,  or  at  least  that  the  most  vigorous  and  there- 
fore the  most  highly  colored  male  will  have  more  offspring.  Wallace's 
contention  that  the  greater  vigor  of  the  male  accounts  for  his  greater 
development  of  plumage  gets  scant  support  from  the  facts  of  castra- 
tion. One  might  rather  contend  that  the  female  must  be  more  vigorous, 
since  she  is  obliged  to  suppress  plumage  that  is  allowed  to  run  riot  in 
the  male. 

Wallace's  argument  in  favor  of  natural  selection  holding  down  the 
plumage  in  the  female  as  a  protection  to  her  while  nesting  might 
appear  to  fit  the  facts  better  were  it  not  that  the  quest  for  an  explana- 
tion of  the  male's  plumage  is  thereby  abandoned.  It  should  not  be 
forgotten  in  this  connection  that  the  nest  is  generally  only  partly 
concealed,  that  bright  color  at  rest  need  not  be  conspicuous,  and  that 
the  male,  exposed  as  he  is  through  a  considerable  part  of  the  year,  still 
manages  to  maintain  himself  in  about  equal  numbers  with  the  female. 
Suppose,  however,  for  the  sake  of  argument,  that  natural  selection  has 
kept  under  the  full  possibilities  of  the  female.  The  modus  operandi 
would  be  competition  between  the  least  adorned  females,  suppression 
being  brought  about  by  the  activity  of  the  ovary;  while  the  male  is 
left  therefore  to  exhibit  the  full  possibilities  of  the  genetic  complex  of 


RELATING    TO    SECONDARY    SEXUAL    CHARACTERS.  83 

his  race  without  restraint.  The  facts  in  the  case  are  that  the  plumage 
of  the  male  is  the  direct  result  of  his  genetic  composition;  th<'  female 
has  the  same  genetic  composition  (the  sex-linked  characters  are  duplex  >, 
but  the  ovary  produces  a  substance  that  holds  them  in  restraint.  Put 
in  this  way,  there  is  nothing  further  to  be  explained,  unless  we  insist 
on  finding  an  explanation  as  to  how  the  species  came  to  have  its 
genetic  constitution.  In  other  words,  if  we  are  not  satisfied  with  the 
statement  as  to  the  actual  situation,  we  must  explain  it  by  a  utili- 
tarian appeal  to  a  relation  between  the  plumage  and  the  world  outside 
of  the  individual  or  the  species.  To  those  who  feel  unsatisfied  to  leave 
the  case  as  it  stands  on  a  physiological  basis,  there  is  another  hypo- 
thetical means  of  escape.  It  may  be  assumed  that  the  genetic  factors 
that  are  instrumental  in  producing  the  secondary  sexual  characters 
have  also  other  but  unknown  influences  in  the  economy  of  the  species, 
color  and  ornamentation  being  by-products  of  these  factors  whose 
utility  in  other  directions  accounts  for  their  presence.  Such  a  philos- 
ophy has  perhaps  one  redeeming  feature,  since  it  suggests  the  possibil- 
ity of  searching  for  other  influences — influences  that  only  incidentally 
give  the  striking  coloration  and  ornamentation  of  the  males. 

At  first  sight  the  absence  of  cock-feathering  in  the  Sebright  may 
seem  to  furnish  the  occasion  for  such  a  quest.  It  might  appear  that 
since  only  one  or  two  genetic  factor  differences  are  responsible  for  the 
"nuptial"  plumage  of  the  male,  that  this  plumage  may  have  originated 
in  one  or  two  genetic  changes.  Such  an  argument  is  fallacious,  how- 
ever, for  very  many  genetic  factors  may  historically  have  been  neces- 
sary to  build  up  the  nuptial  plumage  of  the  male.  The  breeding 
experiment  shows  no  more  than  that  one  or  two  other  factors  have 
appeared  that  counteract  the  effect  of  all  that  the  others  are  capable  of 
producing;  the  experiment  throws  no  light  upon  how  many  or  how- 
few  these  other  factors  may  be.  That  the  nuptial  complex  is  still 
present  in  the  Sebright  is  evident  after  castration.  Castration  shows 
only  that  the  testes  in  the  Sebright  produce  some  material  that  keeps 
down  the  effects  of  all  the  other  factors  combined.  This  conclusion, 
it  is  true,  somewhat  simplifies  the  problem  for  those  who  appeal  to 
natural  selection  as  suppressing  in  the  female  the  feathering  of  the 
cock,  because  it  shows  that  this  could  have  been  accomplished  by  one 
or  two  Mendelian  factors  that  appeared  of  such  a  kind  that  they  caused 
the  ovary  to  produce  a  substance  antagonistic  to  the  influences  Doming 
from  the  genetic  complex  of  the  species. 

With  this  by  way  of  provisional  exposition,  let  us  return  to  the  ques- 
tion as  to  whether  the  Sebright-game  cross  throws  any  other  light  on 
the  possibly  useful  character  of  the  genetic  factor  or  factors  that 
produce  cock-feathering.  It  is  obvious  that  the  evidence  givee  us  no 
clue  at  all,  for  with  the  exception  of  the  normal  allelomorphs  of  the 
dominant   factor   for   hen-feathering,  all   the   other  factors  are   still 


84  THE    GENETIC   AND   THE    OPERATIVE   EVIDENCE 

present  in  the  Sebright.  The  normal  allelomorph  in  question  need 
not  have  had  any  relation  to  the  other  complex;  in  fact,  it  seems  not 
to  have  any,  because  the  castrated  Sebright  (with  both  normal  allelo- 
morphs replaced  by  genes  for  hen-feathering)  still  develops  the  charac- 
teristic cock-feathering. 

The  outcome  in  the  duck  with  its  double  male  plumage  is  still  more 
puzzling  when  we  attempt  to  analyze  the  situation  in  the  light  of  the 
selection  theory.  At  the  height  of  the  breeding-season,  when  his  testes 
are  enlarged  and  functioning  actively,  a  substance  is  being  produced 
that  leads  to  the  eclipse  of  the  nuptial  plumage.  If  the  male  were 
selected  by  his  partner  for  his  plumage,  he  would  be  chosen  for  a 
plumage  that  develops  in  the  absence  of  the  functioning  testes.  If  the 
male  is  chosen  because  of  his  greater  aggressiveness  or  "activity"  or 
"vitality"  due  to  the  development  of  his  testes,  the  result  would  be  to 
select  males  that  would  probably  develop  a  better  eclipse  plumage. 
The  case  is  interesting  because  it  gives  an  opportunity  to  distinguish 
between  a  plumage  that  develops  under  the  influence  of  the  sexual 
organs  and  one  that  does  not;  and  the  latter  is  paradoxically  the 
nuptial  plumage.  It  is  true  that  the  male  might  be  selected  for  his 
nuptial  suit,  and,  theoretically  at  least,  female  choice  might  still  be 
made  responsible  for  this  plumage,  but  this  merely  shifts  the  problem, 
for  it  leaves  "unexplained"  the  appearance  historically  of  the  effect  of 
the  activity  of  the  testes  in  suppressing  this  plumage  for  a  short  time 
after  maturity.  No  doubt  an  attempt  might  be  made  to  show  that 
natural  selection  comes  in  at  this  time  of  the  year  in  giving  a  protective 
color  to  the  male,  but  so  long  as  any  evidence  is  lacking  as  to  the  need 
of  this  protection  the  argument  serves  rather  to  further  complicate  an 
already  difficult  situation. 

Goodale  has  written  to  me  that  there  is  an  account,  in  the  Agricul- 
tural Journal,  Union  of  South  Africa,  iv,  1912,  of  the  effects  of  the 
removal  of  the  ovary  of  the  female  ostrich.  I  have  not  been  able  to  see 
the  account,  but  according  to  my  informant  such  female  individuals 
assume  the  male  secondary  characters. 

Of  unusual  interest  in  connection  with  the  seasonal  change  of  plum- 
age in  males  of  dimorphic  species  are  Beebe's  experiments  with  scarlet 
tanagers  and  bobolinks.  In  both  species  the  males  in  their  nuptial 
plumage  are  very  different  from  the  females.  Full-plumaged  males  of 
both  species,  at  the  height  of  their  "vocal  and  physical  condition," 
were  confined  in  small  cages.  The  supply  of  light  was  gradually  cut 
off  and  a  slight  increase  of  the  amount  of  food  was  allowed  them.  The 
birds  became  less  active  in  consequence  and  increased  in  weight.  ' '  The 
time  for  the  fall  molt  came  and  passed  and  not  a  single  feather  was 
shed."  The  birds  had  skipped  the  autumn  molt  and  remained  in  their 
nuptial  plumage.  The  song  soon  died  away ;  "  the  birds  seldom  uttered 
even  a  chirp."    From  time  to  time  a  bird  was  gradually  brought  into 


RELATING    TO    SECONDARY    SEXUAL    CHARACTERS.  S.j 

the  light  for  a  week  or  two  and  meal-worms  were  added  to  the  diet. 
This  invariably  resulted  in  a  full  resumption  of  song. 

"I  found  that  a  sudden  alteration  in  temperature — either  lower  or  higher — 
wrought  a  radical  change  in  the  physical  metabolism  of  the  bird*.  They 
would  stop  feeding  almost  altogether,  and  one  tanager  lost  weight  rapidly. 
A  few  feathers  on  the  neck  fell  out,  and  in  the  course  of  some  two  weeks  this 
bird  moulted  almost  every  feather  and  came  strongly  into  his  normal  winter 
plumage  of  olive  green.  The  metabolism  set  up  by  the  change  in  temperature, 
in  its  intent  and  rapidity,  seems  comparable  only  to  the  growth  of  a  deer's 
antlers. 

"Early  in  the  following  spring  individual  tanagers  and  bobolinks  were  grad- 
ually brought  under  normal  conditions  and  activities,  with  quick  result ;  just 
as  the  wild  birds  in  their  winter  haunts  in  South  America  were  at  that  time 
shedding  their  winter  garb  and  assuming  the  most  brilliant  hues  of  summer,  so 
the  birds  under  my  observation  also  moulted  into  the  colors  appropriate  to  the 
season.  The  old  scarlet  and  black  feathers  fell  from  the  tanagers  and  were 
replaced  by  others  of  the  same  color;  from  buff,  cream,  and  black,  the  bobo- 
links moulted  into  buff,  cream,  and  black!  There  was  no  exception;  the  moult 
was  from  nuptial  to  nuptial,  not  from  nuptial  to  winter  plumage.  The  dull 
colors  of  the  winter  season  had  been  skipped." 

How  are  these  results  to  be  interpreted?  Obviously  the  environ- 
ment prevented  the  autumn  molting;  hence  the  birds  necessarily 
retained  their  nuptial  plumage.  But  is  this  the  whole  story?  Did  they 
not  also  remain  sexually  active  with  their  testes  producing  sperm  as  in 
the  mating  season?  In  other  words,  if  feathers  had  been  plucked  from 
them,  would  not  the  new  feathers  have  been  like  those  already  present? 
Despite  the  author's  statement  that  not  a  single  feather  was  molted, 
is  it  not  likely  that  occasionally  a  feather  must  have  been  accidentally 
lost.  If  even  one  had  been  lost  and  an  eclipse  feather  had  replaced  it, 
the  effect  would  not  have  escaped  so  keen  an  observer  as  Dr.  Beebe. 
It  seems  to  me  not  unlikely  that  an  occasional  feather  may  have  been 
lost  and  replaced  by  a  nuptial  one.  If  so,  then  the  results  are  most 
probably  interpreted  as  due  to  the  birds  having  remained  sexually 
active.  This  condition  suppressed  the  autumn  molt,  and  at  the  same 
time  would  cause  any  single  feather  lost  to  be  like  those  still  present 
In  support  of  such  a  conclusion  I  can  appeal  to  Beebe's  statement  that 
after  a  week  in  the  light  a  full  resumption  of  the  song  took  place.  It 
is  unlikely  that  sexual  maturity  would  be  attained  in  so  short  a  time 
unless  the  birds  were  already  in  the  condition  of  sexual  vigor.  Perhaps 
one  can  appeal  also  to  Beebe's  other  statement,  viz,  that  after  a  sudden 
change  in  temperature,  followed  by  a  changed  metabolism  and  km  of 
weight,  the  birds  molted  and  assumed  the  eclipse  (winter)  plumage. 
Here  I  should  interpret  the  facts  cited  possibly  to  mean  that  the  males 
lost  their  sexual  activity  and  in  consequence  developed  the  eclipse 

plumage. 

Until  further  information  is  obtained  judgment  must  be  suspended. 
If,  as  Beebe's  statements  strongly  suggest,  the  external  conditions. 


86       THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

acting  directly  on  the  "metabolism,"  cause  the  changes  observed,  then 
the  experiments  mean  that  environmental  conditions  affect  directly 
the  development  of  the  nuptial  and  the  eclipse  plumage;  but  if,  as  I 
suggest  here,  the  effects  observed  are  due  directly  to  the  environmental 
action  through  its  effects  on  the  testes,  then  the  results  fall  more  nearly 
into  line  with  those  of  Goodale  on  ducks,  etc. 

C.  Evidence  from  Amphibia. 

The  thumbs  of  frogs  enlarge  at  the  breeding-season  and  shrink 
afterwards.  The  enlarged  thumb  is  used  by  the  male  in  clasping  the 
female  during  copulation,  and  the  rough  papillae  that  appear  over  its 
surface  at  this  time  may  also  help  to  anchor  the  male  in  his  precarious 
position  on  the  back  of  the  female.  Since  the  pads  and  their  papillae 
are  used  in  copulation,  they  belong  rather  in  the  class  of  accessory 
organs  of  reproduction  than  in  the  class  of  secondary  sexual  characters. 
Smith  and  Schuster  state  for  Rana  fusca  that  the  testes  are  at  their 
smallest  size  in  March  and  April  after  the  breeding-season.  From  that 
time  until  August  they  steadily  increase  in  size  and  reach  their  maxi- 
mum size  in  September.  From  September  to  March  they  are  inactive 
and  full  size,  until  the  shedding  of  the  sperm  in  March  brings  them 
soon  afterward  to  their  lowest  point  again.  It  is  to  be  noted  that  the 
increase  after  March  is  associated  with  the  increase  in  division  rate  of 
the  spermatogonia.    The  ripening  of  the  sperm  is  finished  in  October. 

The  thumb-pads  with  their  pigmented  papillae  are  "cast  off" 
immediately  after  the  breeding-season,  the  thumb  remaining  smooth 
from  May  to  September.  The  reduction  of  the  pad  is  usually  due  to 
the  reduction  of  the  glands  and  the  disappearance  of  the  papillae. 
Smith  and  Schuster  state:  "During  the  months  when  the  most  active 
growth  of  the  testis  is  taking  place  the  thumb-pads  remain  inactive 
and  smooth."  The  implication,  apparently,  is  that  one  ought  to  expect 
the  growth  in  the  thumb  to  take  place  when  the  germ-cells  are  most 
actively  dividing,  if  its  growth  is  connected  with  their  activity;  but 
there  are  no  grounds  for  such  expectations,  because  the  influence  of  the 
gonad  may  have  nothing  to  do  with  the  division  rate  of  the  germ-cells, 
but  rather  with  interstitial  or  other  cells,  and  even  here  less  with  their 
division  rate  than  with  their  period  of  greater  secretive  activity. 

"In  August  and  September  the  epidermal  papillae  begin  to  be  obvious,  and 
from  this  time  onwards  until  about  February  a  continuous  increase  of  the 
epidermal  papillae  and  pigmentation  occurs.  During  the  greater  part  of  this 
time,  when  the  thumb-pads  are  attaining  their  characteristic  rough  and  pig- 
mented appearance,  the  testes  remain  inactive  and  unchanged — a  fact  which 
has  been  too  readily  overlooked  by  writers  on  the  correlation  of  the  primary 
and  secondary  sexual  characters." 

Nussbaum  (1909)  and  later  Meisenheimer  (1911)  found  that  after 
castration  the  thumb-pads  disappear.  Smith  confirms  this  report  in 
all  essential  respects,  although  in  certain  details  concerning  the  papillae 


RELATING    TO    SECONDARY    SEXUAL    CHARACTERS.  S? 

he  does  not  agree  with  the  two  former  observers.  His  result  s  inon •  t  hat 
castration  at  the  breeding-season  is  rapidly  followed  by  the  loet  of  the 
outer  papillated  layer  of  the  thumb-pads,  but  castration  at  any  other 
season  does  not  have  "any  marked  effect,"  the  papillae  remaining  for 
5  months  and  more  in  the  same  condition  as  at  the  time  of  castration. 
The  essential  point  here,  however,  is  that  the  excessive  and  even 
special  development  at  the  breeding-season  does  not  take  place  ner  is 
again  assumed  (apparently),  if  castration  has  taken  place  at  boom 
other  time  of  the  year. 

Smith  and  Schuster's  attempts  to  transplant  the  testes  into  other 
males  or  females  were  unsuccessful,  as  the  testes  degenerate  after  a 
time.    Auto-transplantation  of  the  testes  were  more  successful. 

Removal  of  the  ovary  had  no  effect  on  the  thumbs  of  the  female, 
and  even  the  injection  of  testes  extracts  into  such  females  did  not 
cause  them  to  develop  pads.  Nussbaum  and  Meisenheimer  had 
found  that  transplantation  of  pieces  of  the  testes,  and  even  injection 
of  testes  extract,  into  castrated  frogs  caused  an  enlargement  of  the 
thumb-pads.  Smith  shows  that  this  conclusion  rests  on  uncritical 
evidence.  At  any  rate,  his  own  more  carefully  planned  experiments 
extending  over  the  year  show  that  the  results  obtained  by  Nussbaum 
and  by  Meisenheimer  may  be  accounted  for  on  other  grounds  than  the 
effect  of  the  injection  or  implantation. 

The  following  statement  by  Smith  is  not  without  interest,  since  it 
bears  directly  on  an  important  question  as  to  how  internal  secretions 
may  produce  their  effects. 

"The  deduction,  therefore,  which  has  been  unduly  based  on  Nussl mum's 
experiments,  that  the  testis  of  the  frog  contains  an  internal  secretion,  which, 
on  being  circulated  in  the  blood,  calls  for  the  development  of  the  secondary 
sexual  characters,  either  with  or  without  the  mediation  of  the  nervous  system, 

is  without  experimental  foundation The  fact  that  the  developmental 

cycle  of  the  thumb  depends  for  its  normal  course  on  the  presence  of  normal 
living  testicular  tissue  can  be  equally  well  explained  on  the  theory  that  the 
testicular  cells  enter  into  a  chain  of  metabolic  processes  in  the  body  which  do 
not  pursue  their  normal  course  in  the  absence  of  the  testicular  cells.  This 
disturbance  of  the  normal  metabolic  processes  of  the  body,  resulting  in  the 
failure  of  the  metabolic  organs  of  the  body  to  give  rise  to  their  normal  prod- 
ucts in  normal  quantities,  may  have  the  result  of  inhibiting  the  further  devel- 
opment of  the  secondary  sexual  characters.  The  development  of  these  latter 
characters  may  depend,  therefore,  not  directly  on  the  action  of  an  internal 
secretion  or  hormone  derived  from  the  gonad,  but  on  the  elaboration  of  other 
products  in  other  organs  of  the  body  in  their  due  proportions.  These  sub- 
stances may  be  tentatively  called  'sexual  formative  substances/  but  we  have 
no  reason  for  supposing  that  they  are  entirely  devoted  to  sexual  or  reproduc- 
tive purposes,  and  that  they  take  no  part  in  the  ordinary  metabolic  processes 
of  the  body." 

The  arbitrary  distinctions  that  Smith  here  sets  up  do  not  seem  to 
me  to  contribute  anything  to  the  situation,  and  in  fact  in  the  end  it 
amounts  to  practically  the  same  thing  whether  the    hormone   m 


88  THE    GENETIC    AND    THE    OPERATIVE    EVIDENCE 

directly  on  some  specific  part  of  the  body  or  whether  in  doing  so  it 
acts  on  other  parts  as  well.  While  it  is  more  or  less  customary  to 
limit  the  term  " hormone"  to  substances  that  do  produce  specific 
effects  in  a  particular  organ,  no  one  would,  I  suppose,  deny  that 
a  substance  was  acting  as  a  hormone  if  at  the  same  time  it  acted  on 
other  parts  of  the  body  also,  or  even  if  its  immediate  action  were  on 
some  part  and  its  ultimate  action  on  another  part  of  the  animal. 
Moreover,  there  is  nothing  in  the  evidence  appealed  to  by  Smith  that 
supports  one  rather  than  the  other  contention.  It  is  not  apparent  that 
the  simpler  idea  of  hormone  action  may  not  still  apply.  Failure  to 
implant  the  testes  in  castrated  male  or  female,  and  failure  of  injections 
to  produce  the  results  sought  for,  may  mean  no  more  than  that  the 
experimenter  failed  to  fulfill  some  one  of  the  conditions  present  in  the 
normal  frog  at  the  breeding-season.  Granting  that  the  results  recorded 
by  Nussbaum  and  Meisenheimer  are  open  to  the  serious  objections, 
pointed  out  by  Smith  and  Schuster,  the  facts  recorded  by  all  three 
writers  indicate  that  the  maximum  development  of  the  pad  takes 
place  when  the  testes  are  at  their  greatest  development  and  that  the 
pad  suddenly  decreases  if  at  this  time  the  testes  are  removed.  It 
would  seem  to  follow  that  since  the  swelling  is  connected  with  the 
presence  of  a  certain  condition  of  the  testes,  its  enlargement  is  to  be 
referred  directly  to  the  latter,  and  the  case  comes  under  the  general 
category  of  "secondary  sexual  differences,"  depending  on  the  gonad. 

The  secondary  sexual  characters  of  Triton  cristatus  can  not,  as  can 
those  of  the  frog,  be  supposed  to  be  mechanically  useful  in  mating,  but 
seem  to  be  comparable  in  every  respect  with  the  secondary  sexual 
ornaments  of  higher  animals.  The  work  of  Bresca  has  shown  that  their 
development  is  under  the  influence  of  the  testes.  The  most  important 
secondary  sexual  characters  of  the  male  are  the  dorsal  comb  and  the 
white  stripes  of  the  tail.  The  comb  extends  along  the  dorsal  surface 
of  the  body  and  of  the  tail  (with  a  slight  dip  in  the  pelvic  region).  It 
is  fully  developed  during  the  breeding-season,  when  it  reaches  a  height 
of  1.5  cm.  In  winter  it  is  only  0.66  mm.  high,  or  even  less.  The  white 
stripes  also  are  fully  developed  in  the  breeding-season.  They  extend 
on  each  side  from  the  cloaca  to  the  end  of  the  tail.  In  the  female  the 
white  stripe  is  sometimes  faintly  seen.  The  angles  of  the  tail  and  of  the 
cloaca  thickening  are  black-brown  or  black.  The  belly  of  the  male  is 
bright  orange  or  "Ziegel  rot";  that  of  the  female  sulphur-yellow  or 
orange,  but  the  difference  is  not  constant.  The  upper  surface  of  the 
head  of  the  male  is  marbled,  especially  during  the  breeding-season 
almost  disappearing  during  the  rest  of  the  year.  Bresca  found,  when 
the  testes  were  removed  from  sexually  mature  males,  that  in  the  course 
of  a  year  all  the  important  secondary  sexual  characters  disappeared, 
including  the  comb,  the  white  tail  stripes,  and  the  marbling  of  the 
upper  surface.    Removal  of  the  ovaries  did  not  affect  the  characters  of 


RELATING   TO    SECONDARY    SEXUAL    CHARACTERS.  89 

the  female.     The  black  lower  corner  of  the  tail  in  the  male  is  not 
changed  by  castration. 

When  the  skin  along  the  middle  line  of  the  back  of  the  female  is 
transplanted  upon  the  back  of  a  normal  male  (in  place  of  his  own  cob 
the  transplanted  tissue  develops  into  a  comb.  In  other  words,  under 
the  influence  of  the  testis,  the  dorsal  mid-line  tissues  of  the  female 
change  into  those  characteristic  of  the  male.  When  pieces  of  skin  of 
a  male  with  the  white  tail  stripes  are  grafted  on  the  side  of  the  tail  of 
another  male,  the  stripe  remains,  but  when  grafted  similarly  on  a 
female  the  stripe  slowly  disappears.  The  result  shows  that  its  presence 
depends  on  the  testis. 

A  remarkably  clear  case  of  hermaphroditism  in  amphibians  was 
found  by  V.  la  Vallette  St.  George.  He  found  an  individual  of  Triton 
tceniatus  that  was  outwardly  a  male  with  well-formed  dorsal  comb. 
In  the  interior  were  two  large  testes  in  normal  position  and  just 
lateral  to  these  on  each  side  a  large  ovary.  Sections  showed  ripe  sperm 
in  the  testes  and  typical  ova  in  the  ovary.  Sperm-ducts  were  present, 
but  no  oviducts.  The  presence  of  the  testes  will,  of  course,  account  for 
the  development  of  the  secondary  sexual  characters  of  the  male. 

Other  cases  amongst  the  Anura  have  been  recorded  by  Loisel  and  by 
Marshall,  Spengel,  and  Knappe.  In  the  early  stages  of  the  gonad  in 
frogs  there  appears  to  be  an  hermaphroditic  stage  in  which  egg  mother- 
cells  and  sperm  mother-cells  are  both  present,  at  least  in  those  individ- 
uals that  will  later  become  males  (Kusakowitsch). 

The  normal  hermaphroditism  of  certain  fish  (Serranus)  and  its  rare 
occurrence  in  other  species  (recorded  by  Shattuck  and  Seligmann) 
need  not  be  recorded  here.1 

D.  Evidence  from  Crustaceans. 

In  the  Crustacea  the  secondary  sexual  characters  are  not  marked, 
except  in  a  few  cases.  In  the  amphipods,  Holmes  has  shown  direct 
contact  plays  the  chief  role  in  mating,  and  in  the  crayfish  it  has  been 
shown  by  Dearborn,  Andrews,  and  Pearse  that  sex  recognition  is  largely 
tactile.  Chidester  also  has  shown  this  in  crayfish.  Even  in  crabs, 
and  especially  those  living  on  land  which  have  well-developed  eyes  and 
good  vision,  secondary  sexual  differences  are  as  a  rule  slight  and  the 
mating  instincts  simple.  On  the  other  hand,  the  enormous  chela  of  the 
male  of  the  fiddler  is  supposed  to  be  a  secondary  sexual  difference 
(mainly  because  no  other  use  for  it  has  been  found).  Pearse  suggests 
that  the  waving  of  this  claw  by  the  male  is  used  as  a  sex  signal .  al  t  h.  nigh 
he  is  disinclined  to  accept  Alcock's  view  that  it  has  become  "con- 
spicuous and  beautiful  in  order  to  attract  the  female." 

The  most  remarkable  case  known  of  a  change  in  the  secondly 
sexual  characters  of  one  sex  into  those  of  the  other  was  discovered  by 

1  See  the  latter  also  for  references  to  Lacrrtilia  and  Chclonia. 


90  THE    GENETIC   AND   THE    OPERATIVE   EVIDENCE 

Giard  in  1886.  As  a  result  of  infection  by  parasitic  Crustacea  (e.  g., 
Sacculina),  the  male  crab  develops  the  secondary  sexual  characters  of 
the  female.  It  has  been  generally  supposed,  following  Giard,  that 
this  result  is  due  to  the  destruction  of  the  testes  of  the  male  by  the  roots 
of  the  parasite  that  invades  the  spaces  between  the  organs  of  the 
host,  and,  in  the  case  of  the  testis,  ultimately  brings  about  its  partial 
or  complete  destruction.  Not  unnaturally  the  results  here  were  sup- 
posed to  be  parallel  to  those  of  castration  in  vertebrates,  and  received 
in  fact  the  name  of  "parasitic  castration."  More  recently  Geoffrey 
Smith  has  studied  this  phenomenon  in  the  crab  Inachus,  infected  by 
the  parasite  Sacculina,  and  has  reached  the  conclusion  that  the  change 
is  not  due  to  injury  or  to  destruction  of  the  testes,  but  to  a  change  in 
the  metabolism  of  the  crab  brought  about  by  the  parasite. 

Taking  Geoffrey  Smith's  case  of  Inachus-Sacculina  as  typical,  the 
changes  brought  about  are  as  follows :  The  parasites  attach  themselves 
to  the  young  crabs  before  the  external  secondary  sexual  differences  have 
appeared.  In  the  females,  the  effect  is  to  cause  them  to  develop  pre- 
maturely the  distinctively  female  characters.  In  the  male,  on  the 
other  hand,  the  narrow  abdomen  of  the  male  changes  after  a  molt  into 
the  broad  abdomen  of  the  female,  which  also  develops  ovigerous 
appendages  on  its  ventral  surface  like  those  of  the  female  in  every 
detail.  The  larger  claw  of  the  male  changes  into  that  of  the  female, 
which  is  different  in  form  as  well  as  in  size.  Some  years  ago  I  ven- 
tured to  raise  the  question  as  to  whether  these  effects  on  the  male 
might  not  be  interpreted  as  retention  of  the  juvenile  characters  rather 
than  development  of  the  female  characters  in  the  male.  This  might 
appear  more  especially  the  case  in  the  somewhat  more  juvenile  shape 
of  the  anterior  abdominal  appendages  and  possibly  also  in  the  shape 
of  the  broader  abdomen;  but  Smith  has  later  shown  that  the  results 
can  not  be  interpreted  as  juvenile,  for  when  the  changed  organs  are 
examined  in  detail  they  are  found  to  differ  from  the  same  organs  in 
the  juvenile  condition,  and  to  be  identical  with  those  of  the  adult 
female.  I  think,  therefore,  that  we  must  accept  this  interpretation  of 
Giard  and  of  Smith  as  correct.  But  Smith  goes  further  and  believes 
that  the  effects  may  be  carried  so  far  that  eggs  develop  in  the  old 
testes;  in  other  words,  that  the  testis  changes  to  an  ovary.  It  seems 
to  me  that  the  evidence  to  support  this  last  point  should  be  much 
stronger  than  that  advanced  by  Smith  before  we  can  accept  this 
interpretation,  for  we  lack  the  essential  control  for  this  evidence.  In 
only  a  single  case  were  eggs  found — in  the  testis  of  a  male  that  had  been 
infected,  but  from  which  the  parasite  had  fallen  off,  and  which  was 
presumably  recovering  from  the  effects  of  its  presence.  Now,  it  is 
known  that  in  the  testes  of  some  male  animals  a  few  eggs  may  occa- 
sionally be  found  where  there  is  no  suspicion  that  the  animal  has 
changed  its  sex.  In  some  Crustacea,  in  scorpions,  and  in  insects, 
isolated  instances  of  this  kind  have  been  found.    Abnormal  division 


RELATING   TO    SECONDARY    SEXUAL    CHARACTERS.  91 

of  a  spermatogonial  cell,  of  such  a  kind  that  both  sex  BfaromOMn 
(in  the  case  of  insects  at  least)  got  into  the  same  cell  might  be  expected 
to  cause  such  a  cell  to  become,  even  in  the  male,  an  egg-cell  rather 
than  a  sperm-cell.  The  degenerative  changes  of  the  testes  in  the 
hermit  crab  caused  by  the  parasite  might  be  imagined  to  favor  such 
abnormal  division  with  its  consequences.  More  significant,  however, 
is  the  fact  that  the  parasite  causes  the  absorption  of  the  ovary  when 
it  infects  a  young  female,  so  that  even  all  its  eggs  disappear.  In  other 
words,  the  parasite  is  as  injurious  to  the  peculiarly  female  organ  as  it 
is  to  the  testis.  Why,  then,  one  can  not  but  ask,  should  an  influence 
that  causes  such  effects  on  the  ovary  first  change  a  male  into  a  female 
so  long  as  it  is  present  and  then  when  the  parasite  has  disappeared  leave 
an  influence  behind  of  a  kind  that  causes  the  ovary  to  develop— an 
organ  which  the  parasite  destroys  when  the  parasite  is  present?  Is 
it  not  more  probable  that  only  the  secondary  sexual  organs  were 
changed,  without  change  in  sex,  the  single  case  of  eggs  observed  being 
caused  in  another  way?  This  point  can  only  be  settled  by  direct  exper- 
imentation either  by  removal  of  the  testis,  by  injuring  it,  or  by  inject  i<  m. 
grafting,  or  feeding  experiments.  The  extent  of  the  testis  and  its  posit  ion 
make  it  impossible  to  remove  it  by  an  operation,  as  I  have  found  after 
repeated  attempts.  It  seemed  easier  to  destroy  it  by  radium.  This  I 
have  tried  to  do,  using  very  powerful  tubes,  treating  the  crab  (fiddler 
crabs)  for  several  hours.  The  crabs  had  had  one  claw  removed — the 
enormously  large  one — and  were  kept  until  the  next  molt,  that  occurred 
from  a  week  to  six  weeks  later.  In  none  of  the  cases  was  any  change 
produced.  The  large  claw  of  the  male  regenerated,  of  course,  not  full 
size  after  only  one  molt,  but  after  several  nearly  full  size  and  always 
with  the  peculiarities  of  the  male  crab.  The  abdomen  and  the  appen- 
dages were  not  changed.  Whether  the  significant  cells  of  the  testes, 
if  there  are  such  cells  apart  from  the  germ-cells,  were  destroyed,  can 
not  be  told,  for  as  yet  the  histological  examination  of  the  material  has 
not  been  made.  Until  a  successful  operation  has  been  done.  I  think 
we  must  hesitate  to  accept  Smith's  argument,  although  based  as  it  is 
on  a  series  of  interesting  observations.      His  speculation  is  as  follows. 

"The  reason  why  Sacculina  causes  the  assumption  of  the  adult  feinal- 
in  Inachus  is  found  in  the  facts:  (1)  that  the  roots  of  Sacculina  elaboral 
yolk-substance  from  the  blood  of  Inachus  of  a  similar  nature  to  that  which  is 
elaborated  in  the  ovaries  of  an  adult  Inachus;  (2)  that  in  order  to  elaborate  this 
yolk-substance  the  roots  take  up  from  the  blood  of  Inachus  the  female  sexual 
formation  substance,  which  is  the  necessary  material  for  forming  tin-  yolk 
that  the  female  sexual  formative  substance  being  absorbed  by  the  Sacculina 
roots  is  regenerated  in  excess;  (4)  that  the  presence  of  the  female  formative 
substance  continually  circulating  in  large  quantities  in  die  body-fluids  oJ  the 
infected  crabs  causes  the  production  of  adult  female  secondary  sexual  charac- 
ters, and,  when  the  parasite  dies,  of  yolk-containmp  eggs. 

In  brief,  the  evidence  consists  in  showing  that  in  the  parasite  a  yolk- 
substance  appears,  which  Smith  says  comes  from  the  blood  of  the  crab 


92  THE    GENETIC   AND   THE    OPERATIVE    EVIDENCE 

that  produces  it  under  the  influence  of  the  parasite.  Incidentally,  as 
it  were,  this  is  said  to  be  the  same  yolk-substance  (but  no  sufficient 
evidence  that  it  is  the  same  is  given)  that  the  egg  stores  up  inside  itself, 
and  it  is  assumed  that  it  is  a  formative  substance  that  causes  the  cell 
that  gets  it  (or  contains  it  or  secretes  it — details  are  wanting)  to 
become  an  egg-cell.  It  is  the  excess  of  this  substance  produced  by  the 
male  crab,  while  still  a  male,  under  the  influence  of  the  parasite,  that 
affects  the  abdomen  and  its  appendages  in  such  a  way  that  they  assume 
the  female  condition.  There  are  too  many  assumptions  in  the  argu- 
ment, some  of  which  are  scarcely  of  a  kind  that  our  knowledge  of 
development,  incomplete  as  it  is,  can  allow  us  to  accept  without  more 
direct  evidence  in  their  support,  to  make  this  view  very  plausible. 
Until  better  evidence  is  forthcoming,  I  fail  to  be  convinced  by  Smith's 
interpretation  of  his  facts. 

Into  Smith's  and  Robson's  interesting  observations  on  the  blood  of 
crabs,  described  in  Smith's  later  paper  (part  7,  1911),  it  is  not  necessary 
to  enter  here,  since  the  evidence  taken  as  a  whole  offers  little  further  in 
support  of  his  view  than  had  been  already  assumed.  The  argument  on 
page  263  should  not,  however,  pass  unchallenged.    Smith  says: 

"It  is  clear  that  the  old  and  familiar  idea  of  an  internal  secretion  produced 
by  the  gonad  being  the  stimulus  for  the  development  of  the  secondary  sexual 
character  could  not  be  applied  here,  since  at  the  time  that  the  alterations  in 
the  secondary  sexual  characters  take  place  no  ovary  is  present  to  give  rise 
to  the  required  stimulus.  It  is  suggested,  therefore,  that  in  some  way  the 
stimulus  must  reside  in  the  roots  of  the  Sacculina,"  etc. 

The  argument  seems  to  imply  that,  since  the  secondary  sexual 
characters  of  the  female  can  not  be  produced  by  an  ovary  in  the  infected 
male,  therefore  the  Sacculina  must  take  the  place  of  the  ovary.  But 
why  make  such  a  supposition,  for  if  the  testes  simply  keep  down  the 
development  of  the  female  characters,  as  Giard  supposes,  there  is  no 
need  either  for  an  ovary  or  for  a  Sacculina  to  develop  them.  One  might 
as  well  argue  that  since  the  cock  does  not  develop  the  secondary  sexual 
characters  of  the  hen  that  an  ovary  is  essential  for  their  development — 
which  is  true,  but  not  in  the  sense  implied. 

Stamati  (1888)  states  that  he  attempted  to  remove  the  testes  of 
adult  crayfish  and  apparently  succeeded,  but  since  no  effects  are 
expected  until  after  a  molt  occurs  (that  may  not  take  place  for  two 
years  or  more),  no  results  were  obtained.  Injections  of  the  gonads 
with  an  acid  failed,  since  the  animals  died. 

E.  Evidence  from  Insects. 

In  1899  Oudemans  succeeded  in  finding  a  method  of  removing  the 
testes  and  ovaries  from  caterpillars,  using  a  dimorphic  species,  Ocneria 
dispar,  the  gipsy  moth.  The  results  were  negative;  none  of  the  secon- 
dary sexual  characters  of  the  male  or  female  moths  or  the  accessory 
organs  of  copulation  were  in  the  least  affected  by  the  operation.  The 
castrated  male  copulated  as  readily  with  the  female  as  did  the  normal 


RELATING   TO   SECONDARY    SEXUAL   CHABACTBR8.  '.).; 

male,  while  the  spayed  females  also  behaved  as  normal  individuals  of 
that  sex  behave.  Kellogg,  in  1904,  repeated  the  same  operation  in  the 
silkworm  moth  on  a  small  scale  with  the  same  results.  Kopec  and 
Meisenheimer,  in  1909,  repeated  in  a  more  detailed  way  Oudemai 
work.  A  further  important  addition  was  made  by  Kopec  and  by 
Meisenheimer.  They  transplanted  ovaries  into  a  castrated  male  and 
testes  into  a  spayed  female.  Neither  gonad  produced  any  effect  on 
the  characters  of  the  other  sex.  It  is  interesting  to  note  that  the  te 
underwent  their  normal  development  in  the  body  of  a  spayed  female, 
and  even  in  one  with  the  ovaries  present,  and  that  the  ovary  als<  >  under- 
went normal  development  in  the  body  of  the  male.  In  other  words, 
there  is  no  intolerance  of  the  tissue  of  one  sex  to  the  gonad  of  the  other. 
This  result  is  all  the  more  unexpected,  because  other  observations  have 
shown  that  the  color  of  the  blood,  and  its  chemical  properties,  is  quite 
different  in  the  male  and  female  moths  of  certain  species. 

In  the  case  of  moths,  therefore,  if  these  cases  be  regarded  as  typical, 
the  situation  from  the  point  of  view  of  sexual  selection  is  much  simpler 
than  in  birds  in  the  sense  that  the  secondary  sexual  characters  are 
directly  the  product  of  the  genetic  constituents  of  all  the  cells,  and  not 
influenced  indirectly  by  the  secretions  from  the  testes  or  the  ovaries. 
Sexual  selection,  therefore,  if  it  is  an  agent  in  the  evolution  of  the  dif- 
ferences between  males  and  females,  has  acted  on  the  genetic  complex 
to  produce  these  effects  on  either  sex  without  the  result  being  involved 
in  the  condition  of  the  ovary  or  the  testes. 

Regen  castrated  crickets,  Gryllus  campestris,  in  the  Larval  stages  and 
found  no  effects  on  the  adult  structures.    The  castrated  males  chirped 
like  normal  males  and  mated  with  the  females.    Spayed  females  v, 
like  normal  females;  they  bored  holes  in  the  ground,  but  hid  no  eggs 
in  them,  of  course,  as  the  ovary  had  been  completely  removed. 

The  only  genetic  evidence  in  the  group  of  insects,  outside  of  the 
vinegar  fly,  relating  to  the  secondary  sexual  inheritance  of  the  second- 
ary sexual  characters  is  the  following  important  experiments  made  by 
Foot  and  Strobell : 

The  male  of  one  of  the  bugs,  Euchistas  variolarius,  lias  a  black  spot 
on  the  end  of  the  abdomen — a  spot  that  is  not  present  in  the  female. 
Foot  and  Strobell  crossed  a  female  of  this  species  to  another  hug, 
E.  servus,  that  lacks  the  spot  in  both  sexes.  The  daughters  had  no 
spot,  the  sons  a  faint  spot  less  developed  than  in  voriolarius.  Tfo 
inbred  gave  (in  F2)  249  females  without  a  spot,  107  males  with  a  spot, 
and  84  males  without  a  spot.  The  results  are  explieable  on  the  view 
that  a  single  dominant  Mendelian  factor,  not-sex-linked,  causes  the 
spot  in  the  males,  but  the  presence  of  the  gene  in  the  female  produ 
no  effect.  The  effect,  therefore,  is  Bex-limited,  I  <..  its  expression  is 
determined  by  the  rest  of  the  complex  male  or  female. 

The  very  important  breeding  experiments  carried  oul  by  Gold- 
schmidt  on  varieties  of  the  gipsy  moth  should  be  referred  to  in  this 


94  THE    GENETIC   AND   THE    OPERATIVE   EVIDENCE 

connection,  but  as  I  have  recently  reviewed  these  results  in  the  paper 
on  gynandromorphs  written  in  collaboration  with  C.  B.  Bridges,1  I 
need  only  refer  to  that  account  here. 

[Note  added  April  21,  1919.] 

Shortly  after  the  preceding  paper  was  finished  a  theses  by  A.  P6zard  on  the 
secondary  sexual  characters  of  birds  reached  me.  In  it  the  author  gives  an 
account  of  a  number  of  experiments  that  he  has  made  with  poultry  and  with 
pheasants.  His  description  of  the  changes  that  take  place  after  castration 
are  more  exact  and  more  detailed  than  any  other  so  far  recorded ;  but  in  general 
the  results  obtained  by  Pezard,  through  castration,  are  the  same  as  those 
that  had  been  obtained  by  others.  Castration  of  4  male  silver  pheasants  are 
reported.  No  change  in  the  plumage  results,  although  the  changes  that  take 
place  in  the  comb  and  wattles  are  the  same  in  kind  as  those  observed  in  fowls. 
The  sexual  instincts  and  peculiarities  of  the  voice  and  their  belligerency  are  also 
lost.     Similarly  4  golden  pheasants  that  were  operated  on  gave  the  same  results. 

Three  pheasants  with  mixed  plumage  (Phasianus  colchicus)  were  examined. 
Their  testes  proved,  on  histological  examination,  to  be  imperfectly  developed. 
It  is  not  evident  what  relation  existed  between  the  facts  and  the  mixed  plum- 
age.    The  suggestions  made  by  Pezard  seem  inadequate  to  cover  the  cases. 

Testicular  tissue  transplanted  into  castrated  cocks  whose  comb,  wattles, 
etc.,  had  undergone  retrogressive  changes  brought  about  a  return  to  the  normal 
conditions  after  an  interval  during  which  the  implanted  nodules  had  begun 
to  regenerate. 

Testicular  extract  from  the  cryptorchid  testes  of  swine  was  injected  into 
castrated  cocks.  In  one  case  this  resulted  in  a  rapid  growth  in  size  of  the 
comb,  which,  after  2  months,  had  reached  its  full  size.  Cessation  of  the  injec- 
tions led  immediately  to  a  cessation  of  growth.  Before  injection  the  bird 
exhibited  the  pacifistic  characteristics  of  the  capon,  but  the  injections  brought 
out  little  by  little  the  aggressive  behavior  of  the  normal  male.  The  voice 
reappeared  and  "nous  assistons  a  une  veritable  crise  de  puberte." 

A  histological  study  of  the  testes  of  the  fowl  and  of  pheasants  showed  that 
much  connective  tissue  is  characteristic  of  young  birds.  In  the  adult  cock, 
and  during  the  mating  season  of  the  pheasant,  the  connective  tissue  becomes 
largely  crowded  out  by  the  enlargement  of  the  tubules.  Pezard  concludes 
that  the  "interstitial"  cells  in  birds  have  nothing  to  do  with  the  secondary 
sexual  characters,  but  that  these  come  rather  under  the  influence  of  the  ger- 
minal cycle  of  cells  of  the  testes.  The  submergence  of  the  connective-tissue 
cells  of  pheasants  during  the  breeding-season  and  their  reappearance  during 
the  rest  of  the  year  might  appear  to  have  some  relation  to  the  facts  that  I 
have  recently  described  in  Sebrights,  but  as  the  nuptial  plumage  of  the  male 
remains  the  same  throughout  the  year  we  can  not  ascribe  any  direct  influence 
to  this  tissue.  Nevertheless,  the  different  tissues  of  the  testes  in  birds  that 
show  seasonal  dimorphism  of  plumage  should  be  carefully  examined. 

Pezard  made  a  few  observations  on  hens  whose  ovary  had  been  removed. 
His  results  are  in  accord  with  those  of  Goodale,  except  that  he  thinks  that  the 
ovary  has  no  influence  on  the  erectile  organs  (comb,  etc.)  which  acquire  in  the 
spayed  bird  the  same  length  as  that  of  the  normal  female. 

Two  hens  showing  male  characteristics  and  a  pheasant  similarly  affected 
are  described.  In  all  three  cases  an  examination  of  the  ovary  was  found  to 
be  undeveloped  or  abnormal. 

1  Carnegie  Inst.  Wash.  Pub.  No.  278,  1918. 


RELATING   TO    SECONDARY    SEXUAL    CHARACTERS.  95 

PART   IV. 

SUMMARY  AND  CONCLUSIONS. 

1.  The  two  principal  results  obtained  were:  (a)  that  cast  ration  of 
hen-feathered  Sebright  males  causes  them  to  develop  the  full  plum, 
characteristic  of  the  cock-bird;  (6)  that  complete  hen-feathering  is  due 
to  two  dominant  Mendelian  genes. 

2.  A  striking  change  takes  place  when  the  Sebright  male  is  cad  rated 
(plate  1,  figs.  3,  4;  plate  3,  fig.  1).  The  new  feathers  on  the  upper 
surface  of  the  head,  neck,  back,  wings,  rump,  and  tail-coverts  assume 
a  different  color  and  distribution  of  their  pigment;  they  take  on  a  new 
shape,  and  in  those  regions  where  in  the  cock  the  barbules  are  absent 
from  a  part  of  the  margin  of  the  feather,  the  same  absence  occurs  in  t  he 
castrated  birds.  Such  feathers  are  present  on  the  neck,  back,  wing- 
bow,  and  rump.  The  transition  is  shown  in  the  figures  in  plate  6, 
where  for  comparison  one  of  the  old  and  one  of  the  new  feathers  lie 
side  by  side.  The  tail-coverts  in  the  hen-feathered  bird  are  short,  and 
like  those  in  the  hen  do  not  cover  the  true  tail.  After  castration  they 
become  excessively  long — longer,  in  fact,  than  in  many  cocks — and 
cover  the  true  tail  feathers.  The  tail  feathers  themselves,  moreover, 
become  increased  in  length,  as  do  the  posterior  row  of  feathers  of  the 
wing-coverts.  On  the  breast  and  sides  the  change  is  less  marked.  The 
castrated  Sebright  loses  his  erect  carriage,  but  how  far  this  is  due  to  the 
changes  in  his  plumage  and  how  far  is  real  (as  a  result  of  a  new  balance 
due  possibly  to  the  lengthening  tail  and  its  coverts)  I  can  not  decide. 

3.  While  castration  causes  the  hen-feathered  male  to  make  addi- 
tions in  color,  length,  and  size  of  many  feathers,  it  causes  at  the  same 
time  the  other  retrogressive  changes  characteristic  of  the  capon  (a 
castrated  cock-feathered  bird);  the  comb  and  wattles  shrink  and 
become  pale,  the  birds  almost  cease  crowing,  and  become  timid.  They 
do  not  make  much  effort  to  mate  with  the  hens,  but  when  they  do  they 
show  the  usual  copulatory  reactions. 

4.  If  feathers  are  removed  at  the  time  of  castration,  the  new  feathers 
show  the  full  effect  of  the  removal  of  the  testes,  although  they  must 
have  begun  to  develop  immediately  afterward.  It  is  suggested  that 
by  means  of  this  delicate  test  the  time  relations  of  the  internal  secre- 
tion can  be  profitably  studied. 

5.  Feathers  that  may  have  started  their  development  at  the  time 
of  the  operation  show  the  old  influence  at  the  tip  of  the  feat! 
(plate  10)  and  the  new  one  in  the  rest  of  the  feather.     The  change  is 
abrupt,  although  the  transition  is  perfect. 

6.  Incomplete  castration  of  the  hen-feathered  male  leads  to  smaller 
changes  in  the  same  direction  than  those  following  complete  east  rat  km. 

Where  such  small  pieces  of  the  testis  were  left  that  complete  ooek- 
feathering  followed,  the  bird  slowly  changed  back   to  hen-feat  hering 


96       THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

as  the  testes  began  to  regenerate.     When  the  regenerated  pieces  were 
removed  the  bird  became  cock-feathered  again. 

7.  One  Sebright  male  whose  testes  appear  to  have  been  completely 
removed  did  not  change  the  character  of  the  plumage.  No  testes  were 
found  on  autopsy.  It  is  suggested  that  some  other  endocrine  organs 
have  taken  over  the  function  of  the  testes,  but  as  yet  none  such  can  be 
indicated. 

8.  In  one  case  an  old  hen-feathered  (Fi)  male  began  to  change  over 
to  cock-feathering.  It  was  found  that  his  testes  had  dwindled  (prob- 
ably through  disease)  to  very  small  size  (10  by  5  mm.). 

9.  The  Fi  male  of  the  cross  between  the  Sebright  and  game  is  also 
hen-feathered  (plate  2,  fig.  1).  After  castration  he  becomes  cock- 
feathered  (plate  2,  fig.  4)  and  shows  thereby  the  genetic  type  of  the 
heterozygous  cock-feathered  class  in  which  his  hen  belongs.  The 
change  in  this  male  is  even  more  strking  than  that  in  the  Sebright. 
The  change  in  the  individual  feathers  is  shown  in  plate  7,  figs.  1  and  la. 

10.  Three  types  of  F2  hen-feathered  castrated  males  are  shown  in 
plate  2,  figure  3,  and  plate  3,  figure  3  and  figure  4.  The  first  was 
a  dark  bird  that  changed  to  a  lighter  red  above.  The  third  a  gray 
bird  that  became  bright  red ;  the  second  was  a  light  yellow  that  became 
deep  yellow,  etc.  The  class  of  hens  to  which  such  males  belong,  as 
cock-feathered  birds,  can  thus  be  found  out  by  castration.  In  this  way 
the  F2,  and  back-cross,  hen-feathered  cocks  can  be  classified  with  the 
corresponding  F2  cock-feathered  males. 

11.  In  the  F2  generation,  made  up  of  birds  from  the  direct  and 
reciprocal  crosses  taken  together,  there  were  29  hen-feathered  and 
26  cock-feathered  males.  In  the  back-cross  (Fi  hen  by  game  male) 
the  classes  were  2  and  7.  The  results  seem  in  better  accord  with 
the  assumption  that  two  factors  are  present  in  the  Sebright  that  stand 
for  hen-feathering;  that  either  alone  will  give  hen-feathered  birds 
(intermediate  type?) ,  but  that  both  together  give  the  extreme  type  of 
hen-feathering  seen  in  the  Sebright. 

12.  The  difference  in  color  in  the  two  races  (Sebright  and  Black 
Breasted  Game  bantams)  is  very  great.  The  former  have  almost 
uniformly  laced  feathers,  while  the  latter  has  the  varied  plumage  of 
the  jungle-fowl.  The  game  is  strongly  dimorphic  in  color  and  color- 
pattern  ;  the  Sebright  has  the  same  type  of  coloration  and  pattern  both 
in  the  male  and  female,  but  this  is  deceptive,  as  castration  shows, 
because  the  castrated  male  is  as  strikingly  different  from  the  normal 
Sebright  female  as  is  the  cock  of  other  birds  from  the  hen.  The 
resemblance  of  male  and  female  in  this  race  is  due  to  the  suppression 
of  the  true  male  plumage  by  something  produced  in  the  testes.  There- 
fore the  heredity  of  dimorphism  resolves  itself  here  into  the  problem 
of  the  heredity  of  hen-feathering.  That  the  female  Sebright  has  the 
same  genetic  factors  as  the  male  is  shown  by  the  fact  that  she  trans- 


RELATING  TO  SECONDARY  SEXUAL  CHAHAi  I  1 .1         «.»7 

mils  hen-feathering  in  the  same  way  as  docs  the  male  ami  also  by  the 
fact,  as  Darwin  pointed  out,  that  an  old  female  Sebright  whoee  ovaries 
had  degenerated  developed  not  the  hen-feathered  plumage  of  her  own 
cock,  but  cock-feathered  plumage  like  that  of  most  male  poultry. 

13.  The  color  of  the  Fi  birds  is  shown  in  plate  2,  figs.  1  and  _'.  In 
general,  the  feathers  are  stippled,  black  and  light  yellow  being  the  two 
most  conspicuous  ingredients.  Since  hen-feathering  dominates,  the 
dimorphism  is  absent,  or  at  least  is  so  slight  as  to  not  attract  attention 
— little  more,  in  fact,  than  in  the  Sebright  race.  Thecarriageof  the  male 
is  like  that  of  the  Sebright  male.  The  Fi  male  and  female  are  alike  in 
the  direct  cross  and  the  reciprocal,  or  at  least  no  conspicuous  differ- 
ence is  found  between  the  two  classes  of  hens,  indicating  that  no  imp  >r- 
tant  sex-linked  factors  are  involved  in  the  cross. 

14.  The  F2  birds  show  a  great  variety  of  color  and  pattern,  but  those 
obtained  can  be  approximately  grouped  into  16  classes.  The  clasf 
are,  however,  admittedly  not  uniform,  indicating  minor  factors  not 
here  reckoned  with.  The  classification  of  the  hens  is  easiest ;  the  F2 
hen-feathered  males  can  then  in  many  cases  be  referred  to  the  proper 
classes;  the  F2  cock-feathered  males  can  not  be  accurately  classified 
with  their  corresponding  hens,  except  in  the  case  of  those  that  resemble 
the  two  Pi  males,  the  Fi  male,  and  those  that  castration  experiments 
of  the  hen-feathered  males  have  shown  to  belong  to  certain  hen  t  y: 

15.  Despite  the  admitted  difficulties  of  classification,  it  is  suggested 
that  three  factor-pairs  of  differences  will  cover  the  main  color  clac 
seen  in  the  F2  and  in  the  back-cross.  One  or  two  of  these  seem  to  be 
incompletely  dominant,  since  the  Fi  birds  are  not  like  either  parent  in 
any  single  character,  nor  are  they  like  the  wild  type  in  so  far  as  this  is 
represented  by  the  game. 

16.  A  histological  examination  of  the  testis  of  the  male  Sebright  by 
Boring  and  Morgan  has  shown  that  it  contains  cells  like  those  present 
in  the  ovary  of  all  breeds  of  poultry.  These  cells  are  called  luteal  cells 
by  Pearl  and  Boring,  from  their  resemblance  to  the  cells  of  that  name 
found  in  the  corpora  lutea  of  mammals.  In  the  mammals  similar  cells 
are  supposed  to  produce  internal  secretions  that  act  as  hormones. 
Their  function  in  the  female  bird  is  unknown,  but  the  fact  that  after 
the  removal  of  the  ovary  the  female  develops  the  secondary  sexual 
plumage  of  the  male  suggests  that  some  secretion  from  these  sells 
performs  this  function.  Their  occurrence  in  the  male  Sebright  and  their 
complete  absence,  or  paucity,  in  the  males  of  other  races  supports 
strongly  the  view  that  these  cells  are  concerned  with  the  suppression 
of  the  secondary  sexual  plumage. 

17.  While  in  mammals  the  interstitial  cells  have  been  supposed  to 
produce  an  internal  secretion  that  causes  the  development  of  some  of 
the  secondary  sexual  characters  of  the  male,  and  the  fuller  elaboration 
of  others,  in  birds  no  such  connection  exists,  if  we  except   th. 


98       THE  GENETIC  AND  THE  OPERATIVE  EVIDENCE 

of  the  Sebright.  Castration  of  ordinary  males  does  not  affect  deleter- 
iously  the  secondary  sexual  plumage  (although  it  does  the  comb,  be- 
havior, etc.),  in  fact  may  even  enhance  their  effects.  But,  while  in 
the  mammal  a  secretion  is  necessary  for  the  full  development  of  the 
secondary  sexual  characters,  in  the  Sebright  a  secretion  inhibits  certain 
of  them.  What  element  in  the  ordinary  bird  and  in  the  Sebright 
causes  the  full  development  of  the  comb,  wattles,  sexual  behavior,  etc., 
is  not  known.  Possibly  it  is  the  sexual  elements  themselves,  but 
possibly  it  is  a  secondary  influence  of  the  luteal  cells  producing  a  con- 
trary effect  on  these  parts  from  its  effects  on  the  feathers ;  but  possibly 
more  than  one  kind  of  secretory  cell  is  present  in  the  testis  of  the  cock. 

18.  The  causes  of  the  development  of  the  secondary  sexual  characters 
are  seen  to  be  of  such  diverse  physiological  kinds  that  one  may  well 
hesitate  to  apply  the  same  explanation  as  to  their  evolution.  In  fact, 
it  is  pointed  out  that  several  of  the  theories  that  have  been  suggested 
run  counter  to  the  conditions  that  bring  about  the  development  of  the 
secondary  sexual  characters. 

19.  An  attempt  is  made  to  give  a  critical  review  of  Darwin's  theory 
of  sexual  selection  in  the  light  of  the  modern  genetic  and  operative 
results  on  the  secondary  sexual  characters  of  the  vertebrates.  It  is 
pointed  out  that  far  from  extending  the  general  theory  in  its  applica- 
tions, the  modern  work  has  shown  in  the  first  place  that  the  underlying 
conditions  that  call  forth  the  development  of  the  secondary  sexual 
differences  are  so  diverse  in  the  different  groups  of  animals  that  it  is 
a  priori  very  unlikely  that  this  evolution  can  have  been  directed  by  the 
same  external  agent,  such  as  the  choice  of  the  female,  for  such  an 
assumption  carries  with  it  in  several  cases  other  implications  concerning 
the  causes  of  the  suppression  of  these  same  characters  in  the  female 
herself,  etc.  In  the  second  place,  it  is  pointed  out  that  the  problem  of 
the  excessive  development  of  certain  characters  in  the  male  whose 
genes  are  present  in  both  sexes  no  longer  oppresses  us  as  it  did  Darwin, 
for  it  has  been  shown  both  by  the  genetic  and  by  the  operative  work 
that  a  single  factorial  difference  may  be  at  the  root  of  exceedingly 
great  differences  in  the  individual.  Such  results,  while  they  admittedly 
do  not  in  most  cases  tell  us  that  the  differences  involved  have  arisen 
at  a  single  progressive  step,  show  us  nevertheless  that  such  differences 
may  depend  on  very  simple  initial  differences,  and  if  so,  the  entire 
problem  becomes  enormously  simplified.  To  Darwin  the  excessive 
development  of  color  and  ornamentation  appeared  due  to  a  long,  slow 
process  of  evolution  laboriously  brought  about  by  the  female  through 
selection  of  those  males  a  little  more  ornamented  than  their  fellows. 
To-day  we  have  found  out  that  in  many  cases  the  genetic  composition 
of  a  male  with  such  ornamentation  and  of  a  female  without  it  may  be 
almost  identical,  except  that  the  genes  in  one  chromosome  are  duplex 
in  one  sex  and  simplex  in  the  other.    Owing  to  this  initial  difference,  the 


RELATING   TO    SECONDARY    SEXUAL   CHARACTER  99 

female  in  birds  produces  an  internal  secretion  that  Buppn  in  her 

the  ornamentation  shown  by  the  male,  and  in  the  mammal  an  internal 
secretion  produced  by  the  testes  causes  the  full  development  in  the  male 
of  the  secondary  sexual  characters.    If,  as  seems  probable,  th<  re- 

turns are  some  particular  kind  of  substance,  the  condition  thai  led  to 
their  appearance  historically  need  not  have  been  very  complex;  and 
if  not,  the  problem  appears  simplified.  It  still  remains  to  give  Borne 
reasonable  explanation  as  to  why  such  substances  should  continue  to 
be  produced  if  their  products — the  secondary  sexual  characters 
possess  no  "beauty"  for  the  female.  Here  more  work  is  necessary, 
but  the  modern  genetic  point  of  view  may  possibly  give  an  important 
clue.  We  are  coming  to  realize  more  fully  that  the  hereditary  genes 
generally  have  more  than  a  single  effect  on  the  characters  of  the  animal. 
The  secondary  sexual  characters  may,  then,  be  only  by-products  of 
genes  whose  important  function  lies  in  some  other  direction.  If,  for 
example,  the  secretion  produced  by  the  cells  of  the  male  have  an 
important  influence  on  his  output  of  energy,  or  strength,  or  activity, 
their  secondary  influence  over  certain  parts  of  the  body  would  not  call 
for  any  further  explanation  on  the  modern  view  of  natural  selection. 
If  the  secretions  of  the  ovary  of  the  female  bird  have  some  direct  rela- 
tion to  her  physiological  processes  that  are  important  in  the  develop- 
ment of  the  oviduct,  for  instance,  it  would  be  a  matter  of  no  importance 
from  an  evolutionary  point  of  view  if  that  same  secretion  suppree 
in  her  the  development  of  the  high  color  shown  by  the  male. 


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DESCRIPTION  OF  PLATES. 


Plate  1. 


Fig.  1.  Black -Breasted  Game  bantam  cock.  He  is  typically  cock-feathered,  but,  as  in  all 
games,  his  hackles  and  tail-coverts  are  shorter  than  in  the  cocks  of  other 
breeds.     The  comb  was  dubbed  by  the  breeder. 

Fig.  2.  Black-Breasted  Game  bantam  hen.  The  great  contrast  in  color  between  the  cock 
and  hen  is  practically  the  same  as  that  in  the  Brown  Leghorn,  in  most  races 
of  Tosa  fowls,  and  in  the  wild  type  Gallus  bankiva. 

Fig.  3.  Sebright  cock,  "hen-feathered."  The  short  hackles,  the  rounded  feathers  of  the 
back  and  saddle,  and  the  shortness  of  the  tail-coverts  are  characteristic 
features  of  these  males.  For  details  of  individual  feathers  from  different 
regions  see  plates  6  and  8. 

Fig.  4.  A  castrated  Sebright  male.  The  drawing  was  made  about  a  year  after  the  opera- 
tion. This  particular  bird  developed  a  lighter  color  than  did  other  castrated 
Sebrights  (see  plate  3,  fig.  1).  The  entire  dorsal  region  has  changed  its  color, 
and  the  feathers  have  also  changed  in  shape,  length,  etc.  Note  especially 
the  very  long  hackle  and  saddle  feathers  (for  details  see  plate  6,  fig.  la)  and  the 
change  in  the  wing-bow.     The  tail-coverts  have  also  grown  long. 

Plate  2. 

Fig.  1.  Fi  hen-feathered  male  out  of  Game  by  Sebright.    The  hen-feathering  in  this  bird  is 

as  complete  as  in  the  Sebright. 
Fig.  2.  Fi  female  out  of  Game  by  Sebright. 
Fig.  3.  Castrated  male  originally  hen-feathered  (292),  nearly  black  in  color,  as  shown  by  the 

individual  feathers  of  plate  7,  figure  2.     After  castration  the  bird  has  become 

red  above,  with  black  iridescent  tail-coverts,  and  deeper  yellow  (or  red)  below. 
Fig.  4.  Castrated  Fi  male,  originally  like  figure  1.     Note  especially  the  change  in  color  of 

the  whole  upper  surface  that  has  become  red,  like  that  of  the  jungle-fowl. 

The  tail-coverts  have  grown  long  and  are  now  iridescent  black.     The  breast 

has  changed  least,  but  is  a  richer  yellow.     The  comb  and  wattles  and  ear 

lobes  are  shrunken,  as  in  all  capons. 

Plate  3. 

Fig.  1.  A  castrated  Sebright  male.  The  operation  was  performed  on  a  juvenile  bird;  the 
drawing  was  made  a  year  later.  The  bird  is  typical  as  to  the  change  in  color 
that  takes  place  in  the  Sebright.  He  was  darker  red  than  the  bird  shown 
in  plate  1,  figure  4.  The  red  was  more  mahogany  than  the  picture  shows. 
The  original  feathers  were  like  those  in  plate  6,  fig.  2  (there  erroneously 
referred  to  as  those  of  light-colored  Sebright) . 

Fig.  2.  An  F2  hen-feathered  very  dark  male.  The  condition  of  his  plumage  at  the  time  of 
the  operation  is  shown  in  this  figure.  The  change  that  took  place  after  castra- 
tion is  shown  in  the  next  figure. 

Fig.  3.  The  change  that  took  place  in  the  bird  drawn  in  figure  2  is  shown  here.  The  whole 
upper  surface  has  become  red,  except  the  tail-coverts,  which  are  iridescent 
black.  Note  also  the  change  in  color  on  the  wing-bow.  For  the  details  of  the 
feathers  see  plate  9,  figures  1,  la. 

Fig.  4.  A  castrated  F2  bird  that  had  been  hen-feathered  and  had  changed  over  to  cock- 
feathering,  as  shown  here.     The  color  and  the  details  of  the  original  hen- 
feathering  are  shown  in  plate  9,  figures  2  and  2a. 
106 


DESCRIPTION   OF   PLATES.  K)7 

Plate  4. 

Fig.  1.  One  of  the  original  Black-Breasted  Game  males  used  in  the  breeding  eanerimi 

Compare  with  colored  drawing,  plate  1,  figure  1. 
Fia.  2.  A  Black-Breasted   Game  hen  used  in  the  breeding  experiments.     CompSTC  with 

colored  drawing,  plate  1,  figure  2. 
Fig.  3.  A  Sebright  male.     The  bird  was  used  in  the  later  back-crosses  and  not  in  the  origin.il 

experiments.     He  is  typical  of  his  breed. 
Fig.  4.  A  Sebright  female.     One  of  the  birds  used  in  the  original  experiments. 
Fig.  5.  An  Fi  male.     This  bird  had  just  reached  maturity  and  was  younger  than  the  one 

drawn  in  plate  2,  figure  1. 
Fig.  6.  An  Fi  hen  of  the  same  age  as  the  last.     The  pattern  changed  a  little  as  the  hir-1 

became  older. 

Plate  5. 

Fig.  1.  An  adult  Sebright  male  for  comparison  with  the  next  figure. 

Fig.  2.  A  castrated  Sebright  male.     This  photograph  shows  the  same  bird  from  v.  hiell  the 

drawing,  plate  1,  figure  4,  was  made.     It  is  the  lighter  colored  bard  refemd 

to  in  the  text. 
Fig.  3.  One  of  the  two  Fi  castrated  birds.     For  comparison  see  the  colored  drawing  in 

plate  2,  figure  4. 
Fig.  4.  A  castrated  Sebright.     This  bird  is  darker,  and  in  this  sense  more  typical  than 

figure  2. 
Fig.  5.  One  of  the  castrated  Sebright  males  which  at  one  time  after  castration  was  as 

extremely  cock-feathered  as  figure  2,  but  slowly  "went  back"  towards  ! 

feathering,  as  the  figure  shows  especially  in  the  hackle  and  saddle.     The 

details  are  much  better  shown  in  the  feathers  photographed  in  plate  8,  Ggurefl 

1,  2,  3,  4,  la,  2a,  3a,  4a,  16,  26,  36,  46. 
Fig.  6.   The  same  bird  was  opened  and  the  regenerated  pieces  of  the  testis  removed.     He 

returned  later,  as  shown  here,  to  full  cock-feathering. 

Plate  6. 

Figs.  1,  1a.  Typical  old  (1)  and  new  (la)  feathers  (after  castration)  of  the  same  bird.  This 
is  the  "fighter"  male  drawn  in  plate  1,  figure  4,  and  photographed  in  plate 
5,  figure  2. 

Figs.  2,  2a.  Typical  old  (2)  and  new  (2a)  (after  castration)  feathers  of  another  Sebright. 
This  bird  developed  after  castration  darker  feathers  than  did  the  last  bird. 
Its  feathers  were  more  like  those  that  other  castrated  Sebrights  develop 
Legend  on  plate  6  erroneous  as  far  as  2  and  2a  are  concerned. 

Plate  7. 

Figs.  1,  1a.  Typical  old  (1)  and  new  (la)  (after  castration)  feathers  of  an  Fi  bird.     (See 

plate  2,  figures  1  and  4.) 
Figs.  2,  2a.  Typical  old  (2)  and  new  (2a)  (after  castration)  feathers  of  bird  shown  in  plate 

3,  figures  2  and  3  (No.  292). 

Plate  8. 

Typical  feathers  of  "dark"  Sebright  (1,  2,  3,  4)  that  after  incomplete  castration  ehonfed  to 
cock-feathering  (la,  2a,  3a,  4a),  then  later,  as  pieces  of  the  testei  that  had  ! 
left  behind  in  the  old  situs  regenerated,  began  to  go  back  toward-  hen- 
feathering  (16,26,  36,  46).  The  bird  was  then  opened  .main, and  the  re^-n.  r- 
ated  pieces  removed,  when  it  again  became  cock-feat  bend  (1«,  26,  3c,  4c), 
and  has  so  remained  for  more  than  a  year. 


108  DESCRIPTION  OF  PLATES. 

Plate  9. 

Figs.  1,  1a.  Typical  feathers  of  hackle  and  saddle  from  hen-feathered  bird  (No.  68) 

plate  3,  figure  2,  that  changed  over  to  the  cock-feathered  bird  of  plate  3, 
figure  3. 

Figs.  2,  2a.  Typical  feathers  of  an  Fi  male  (2)  that  changed  over  partly  as  a  result  of  degen- 
eration of  his  testes,  into  a  cock-feathered  bird  (2a)  .  The  change  was  not  so 
great  as  it  is  after  castration. 

Figs.  3,  3a.  Typical  feathers  of  Sebright  male  that  slightly  changed  towards  cock-feathering 
(old  hackle  feather  missing). 

Plate  10. 

Figs.  1,  1a.  Old  (1)  and  new  (1a)  wing-coverts  of  normal  Sebright  (1)  and  castrated  (1a). 
Figs.  2a,  2b.  Upper  row,  to  right,  "Transitional"    hackle  feathers    (2a),  and   a  slightly 

later  changed-over  feather  from  wing-bow  (2a),  and  from  back  (2b).     Second 

row,  to  left,  old  (2),  transitional  {2a),  and  changed-over  feather  (26),  from 

saddle  of  Sebright. 
Fig.  3.  Three  feathers  (tail-covert,  wing-bow,  and  saddle)  of  an  F2  hen-feathered  game-like 

male. 
Fig.  4.  A  series  of  breast  feathers  from  an  F2  bird.     At  one  end  of  the  series  (the  left)  the 

feather  is  spangled,  at  the  other  barred. 
Fig.  5.  A  series  of  breast  feathers  from  another  F2  bird.     At  one  end  of  the  series  (the 

left)  the  feathers  are  penciled,  at  the  other  end  they  are  barred. 


T.   H.   MORGAN 


1.  Black  Bre  isted  •  lam<    Banl   m 

2.  Female. 


T.  H.   MORGAN 


1.  lien- feathered   Fj   male. 

2.  Fj  female. 


T.   H.    MORGAN 


PLATE    3 


1.  Castrated  Sebright  male. 

2.  F,  Hen-feathered  male. 


■ 


MORGAN 


PI  A 


1.  Black-Breasted  <  lame  male. 
:>.  Sebrighl  male. 
5.  Hybrid  male. 


2.   I 
- 
6.  Hybrid  i 


MORGAN 


2 


3 


.) 


1.  Adult  Sebright  male 

3.  Castrated  F,  male 

5.  Castrated  Sebrigb.1  male  with  > 


T.    H.    MORGAN 


PLA^ 


Feathers    of    •light"    colored    E 
after  castration   i  I ■<.  2a). 


T.   H.    MORGAN 


E   7 


Saddle 


■ 


Feathers    of    F,    hen- feathered    male 

Feathers   of   a   darker   hen-feal 


T.   H.    MORGAN 


A* 


• 


thers   from  hen-  feathered  in  ' 
feathered  male  (I1.  2a,  after 

testes    regenerated    (  l\   2b,   3b,    l! I  .    then    cl 
castration    (lc.  2C, 


r.   H.    MORGAN 


Hackle  Bad 


II, • 


Feathers   showing   complete    (1)   01 
feathering  to  cock-feathering   < 


T.    H.   MORGAN 


•     10 


\ 


Covert 


2a 


Saddle 


^^ 


Hackle 


Br< 

Normal.  1,  2;  transitional,  la,  2a,  and  changed 
3,  4   and  5.     Feathers    from    F.   birds. 


\ 


623  BE  br  2515 

02/17/97  41245     , . 


